Breast Cancer: Update on Targeted Therapy

A Vindico Medical Education CME activity on HemOncToday.com

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Introduction Predictors of Response to Therapy Recent Advances in Targeted Therapy for Breast Cancer Key Abstracts SABCS 2007 Adjuvant Chemotherapy for Breast Cancer Predicting Risk of Recurrence After Adjuvant Therapies in ER-positive Breast Cancer Update on Endocrine Therapy Looking to the Future

Introduction

At the close of the 2007 San Antonio Breast Cancer Symposium, a panel of specialists gathered to discuss their approach to the clinical and scientific aspects of breast cancer and treatment. During the meeting, the faculty were awestruck by how quickly the awareness of the heterogeneity of breast cancer has percolated from scientific studies into clinical thinking about this disease. Increasingly, oncologists are looking at clinical trials and clinical treatment paradigms developed specifically for various subsets of breast cancer patients, usually defined by hormone receptor, estrogen-receptor (ER) and progesterone-receptor (PR), and by HER2 status.

These classifications have already entered the more common treatment guidelines. The National Comprehensive Cancer Network guidelines for 2007 separate hormone receptor positive and negative and HER2-positive breast cancer. Within each of these different clusters, specific treatment algorithms then take into account tumor size and nodal status. Clinicians have seen a complete inversion of the guidelines where we have gone from pathologic staging to biology to treatment, to biology then pathologic staging and then treatment.

It is astonishing to see how quickly this has taken place. This shift has been driven by advances in molecular biology that have provided insight into the depth of the differences between these cancers, and it has also been driven by clinical observations and new drugs. In particular, trastuzumab forced the cleavage into the HER2-positive or negative; clinicians were already treating patients based on endocrine therapy for ER and PR. These developments caused a major change in the approach to breast cancer.

One of the key areas of excitement in the clinical research arena has been molecular predictors of response to therapy. Practitioners have known for a long time that hormone therapy response is predicted by ER status, and trastuzumab-based and other HER2-based therapy responses are informed by HER2 status. More is known about some of the other predictors of response to therapy. Oncologists know, for instance, that many high-grade tumors are more likely to respond to chemotherapy; hormone receptor negative tumors might be more likely to respond to chemotherapy. But there has been a challenge in determining which tumor is likely to respond to which particular treatment.

The presentations and discussions that took place during this expert panel review were used to develop this monograph sponsored by Vindico Medical Education. Key abstracts on topics not mentioned within the discussion, along with faculty comments, have also been included.

Harold J. Burstein, MD, PhD
Course Director

	Harold J. Burstein, MD, PhD, Course Director, Assistant Professor of Medicine, Harvard Medical School, Dana-Farber Cancer Institute, Boston, Massachusetts.		Carlos L. Arteaga, MD, Vice Chancellor’s Chair in Breast Cancer Research; American Cancer Society Clinical Research Professor; Professor of Medicine and Cancer Biology; Director, Vanderbilt Breast Cancer Program, Nashville, Tennessee.
	G. Thomas Budd, MD, Professor of Medicine, Cleveland Clinic, Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio.		Pamela N. Munster, MD, Associate Professor, Division of Interdisciplinary Oncology, University of South Florida; Scientific Director, Comprehensive Breast Program; Co-Chair, Phase I Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida.
	Lajos Pusztai, MD, Associate Professor of Medicine, Breast Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas.

Predictors of Response to Therapy

With recent advances in the treatment of cancer, including the development of new targeted therapies, there is increased emphasis on the importance of identifying molecular markers to predict treatment response and outcomes. The goal of the use of molecular markers is to improve assessment of prognosis (i.e., outcome in the absence of systemic therapy) and sensitivity to specific agents (or drug regimens), thereby allowing individualization of therapy. The recent 2007 update of the American Society of Clinical Oncology (ASCO) recommendations for the use of tumor markers in breast cancer expanded its list of recommended molecular markers for treatment selection to include estrogen (ER) and progesterone receptors (PR). The recommendations also included the use of Oncotype DX (Genomic Health, Redwood City, Calif.) testing for selection of patients who might benefit from adjuvant endocrine therapy and HER2 to select patients for trastuzumab therapy.¹ Numerous other molecular marker studies have been reported that claim to predict drug sensitivity or prognosis in a variety of tumors, including breast cancer.^2,3 However, most of these studies have been limited by small sample size, heterogeneity of patients, and therapies.⁴ Large, prospectively designed validation studies will need to be performed to define the true operating characteristics and clinical value of these emerging tests.⁴

Genomic Studies: Strengths and Limitations

Advances in genomic technologies have allowed simultaneous examination of multiple genes. High-throughput gene expression profiling has been proven useful in classifying breast cancer and predicting prognosis and sensitivity to therapy.^4-8 Moderately accurate prognostic signatures have been developed, including MammaPrint (Agendia, Amsterdam, Netherlands) (70-gene signature), Veridex/Rotterdam (Johnson & Johnson, Warren, NJ) (76-gene signature), and genomic grade index (GGI).^7,9,10 These and similar tools were developed to allow oncologists to identify patients with ER-positive cancer who have a good prognosis with endocrine therapy.^11,12 Gene signature–based assays also confirmed the clinical observations that ER-negative, high genomic grade basal-like breast cancers are more sensitive to chemotherapy than other cancers.

High throughput gene expression profiling has been proven useful in classifying of breast cancer and predicting prognosis and sensitivity to therapy.

Gene expression profiling is also commonly used as a research tool to attempt to identify predictive markers in phase 2 clinical trials. The rationale for this approach is that analysis of thousands of genes in tumor samples using a semiquantitative and unbiased method should detect an association between response to therapy and the expression of at least some genes. However, there are several reasons why this approach to predictor identification may be limited in yielding reliable results from a typical phase 2 study. Comparison of a large number of variables (genes) generated by microarray analysis between small data sets (i.e., numbers of patients) inevitably leads to many results with small P values, the majority of which result from chance. This problem is exacerbated in studies with small sample sizes and in which response rates are also low. Additionally, individual genes are not independent variables, but rather a large number of genes are expressed concordantly, and these large scale gene expression patterns are also highly correlated with clinical phenotypic characteristics including ER status and grade.^13-16 These clinical characteristics correlate with prognosis and response to treatments. Therefore, the process of predictive marker identification in small studies can be profoundly biased toward discovering genomic equivalents of clinical phenotype.

Gene Profiling

A case study of marker discovery by Pusztai and colleagues illustrates the difficulties of using gene profiling in discovering response predictors to molecularly targeted agents. The study found that the chances were low that gene expression profiling conducted in the context of a single phase 2 clinical trial would detect HER2 mRNA overexpression as a predictor of response to trastuzumab.¹³ The analysis was conducted on gene expression data from simulated phase 2 studies using actual breast cancer gene expression results. To simulate a 60-patient phase 2 study, 45 HER2 normal and 15 HER2 gene-amplified cases were randomly selected from 132 newly diagnosed breast cancer cases with complete gene expression profiles and routine HER2 assessment results. To simulate an 8.3% overall rate of response for the entire study population and a 33% response rate in the HER2 positive patients, five of the 15 truly HER2-amplified (by FISH) cases were deemed trastuzumab “responders” and 10 HER2-amplified and the 45 HER2 normal cases were deemed “nonresponders.” The gene expression profiles of the responders were compared with the nonresponders to detect differentially expressed genes and this was repeated 50,000 times on randomly selected sets of 60 cases from the pool of 132 patient cases. Comparisons were performed by unequal variance t-test and genes were ranked by P value. The objective was to determine how often HER2 was ranked by its P value as the most differentially expressed gene in the 50,000 iterations of the test.¹³

The process of predictive marker identification in small studies can be profoundly biased toward discovering genomic equivalents of clinical phenotype.

HER2 was ranked as the most differentially expressed gene in about 4% of tests and was in the top 10 and 50 expressed genes in approximately 10% and 20% of tests, respectively. These results suggest that any single 60-patient, phase 2 study would have about a 4% chance to identify HER2 as the most predictive gene. This supervised marker discovery effort had low power to discover HER2 as the correct predictor because, in any randomly selected 60 patient data set, many genes have lower P values than HER2 and will be ranked higher. Although HER2 is a robust predictor of response as demonstrated by its significant and consistent overexpression in responders when a single hypothesis is tested (i.e., HER2 mRNA expression is significantly (P<.05) greater in responders compared to nonresponders), when 14,000 other genes are also measured, many will have a greater degree of differential expression in any single study.¹³

Marker Discovery Studies

The preceding case study in marker discovery illustrates some of the challenges facing marker discovery efforts in relatively small phase 2 studies of targeted agents. However, marker discovery studies with standard chemotherapy regimens represent an easier task because of the large scale gene expression differences between the ER-negative/high-grade tumors and the ER-positive/lower grade cancers that are also generally less chemotherapy sensitive than the former. A recent study evaluated a multigene predictor of pathologic complete response (pCR) to a preoperative chemotherapy regimen of paclitaxel and fluorouracil, doxorubicin, and cyclophosphamide (T/FAC) in 133 patients with breast cancer. Pretreatment gene profiling was performed on all patients. Response predictors were developed from 82 cases and 51 independent cases were used to assess the accuracy of these results. Treatment resulted in pCR in 26% of patients and residual disease in 74%. The best performing 30-gene predictor of pCR showed high sensitivity, predicting 92% (12/13) of patients who achieved pCR and high-negative predictive values (96%) in the 51 independent cases. The genomic pCR predictor had higher sensitivity than a clinical variable–based predictor including age, tumor grade, and ER status.⁵ The accuracy of this 30-gene pharmacogenomic predictor to preoperative T/FAC chemotherapy was further evaluated in a study including 74 patients. The genomic prediction results correlated closely with residual cancer burden as a continuous measure of residual cancer after neoadjuvant chemotherapy. It had an overall accuracy of 76% and a specificity of 92% for patients who will end up with extensive residual disease.¹⁷

However, first-generation pharmacogenomic response predictors such as the 30-gene predictor mostly capture information on tumor grade and ER status. This is illustrated in Table 1, which compares receiver operating characteristic curves for the 30-gene pharmacogenomic predictor set, a predictor based on clinical variables (ER, grade, age), and a combined clinical and pharmacogenomic prediction model. The pharmacogenomic predictor set used in this study still provides a small advantage over the clinical predictor set by defining ER and tumor grade more accurately.

The next generation of genomic response predictors will need to be developed separately for ER-negative and ER-positive patients in order to minimize the confounding effect of ER and grade. Also, because trastuzumab is now routinely included in the adjuvant (or neoadjuvant) treatment of patients with HER2-positive breast cancer and it dramatically increases sensitivity to chemotherapy, genomic chemotherapy response predictors will need to focus on the HER2-normal population.

Innovative Approaches in Genomic Response Predictor Discovery

For most new drugs, including new molecularly targeted agents, a blind search for molecular response markers may not be needed. Predictors can be proposed based on mechanism of action or could potentially be developed in preclinical models during the drug development process. Predictors may also be defined retrospectively from analysis of large clinical trials. These putative predictors can be tested prospectively in clinical trials similar to the way drugs are tested. In the same case study of marker discovery that found a low probability of detecting HER2 expression predictive of response to trastuzumab, an alternative scenario was also tested. HER2 mRNA expression as a single gene marker was examined as an a priori defined potential predictor of response to trastuzumab therapy. Using the same t-test as described above, the chances of HER2 being significantly overexpressed among responders in any one of the simulation studies was very high. Histograms of observed P values are shown in Figure 1. These results indicate that 99.6% of histograms were P<.05. Therefore, HER2 overexpression as a predictor of response could have been easily identified by any single trial among the 50,000 simulations.¹³

HER2 overexpression is possible predictor of response to trastuzumab Figure 1. Histogram of P values of HER2 mRNA differential expression in data from 50,000 simulated phase 2 trials. CLINICAL CANCER RESEARCH. ONLINE by Pusztai. Copyright 2007 by American Association for Cancer Research. Reproduced with permission of American Association for Cancer Research in the format Pamphlet via Copyright Clearance Center.

Motivated by these results, a tandem, two-stage phase 2 trial design has been proposed as a method to prospectively evaluate potential molecular markers of response in the clinic (Figure 2). Similar trial designs have been used widely to evaluate drugs and determine whether an agent warrants further phase 3 evaluation. The objectives of the proposed phase 2 marker evaluation trial are to find out (1) whether the drug has a targeted level of activity in a population of unselected patients and (2) if it lacks this level of activity, whether a particular method of patient selection may increase the number of responders, resulting in achievement of the desired level of activity in molecularly selected patients.¹³

Tandem trial design Figure 2. Schema of the tandem two-step phase 2 predictor marker evaluation trial design. CLINICAL CANCER RESEARCH. ONLINE by Pusztai. Copyright 2007 by American Association for Cancer Research. Reproduced with permission of American Association for Cancer Research in the format Pamphlet via Copyright Clearance Center.

Such a study would begin as a classic two-step phase 2 trial conducted in an unselected population with a rule for early stopping. If the predefined rate of response was achieved during the first step, the second step would begin to assess response more precisely in a larger unselected population. However, if the desired rate of response was not met, the trial would continue as a second two-step phase 2 study in only patients who are positive for the amputative response marker. If the level of response in this molecularly defined subset was insufficient after accruing the first “n” patients, this marker arm would be discontinued. However, if the rate of response was sufficient, accrual of marker-positive patients would continue to complete the second step of the study to define the rate of response more precisely in the molecularly selected population.¹³

The advantages of this tandem, two-stage phase 2 trial design include its ability to estimate response rates in both unselected and selected patient populations. In addition, the design allows evaluation of multiple predictors for the same drug and also several different drugs in multiple parallel arms. These predictors can be assessed simultaneously but independently. A multi-arm design is favored to maximize treatment. Importantly, such a trial design efficiently discards candidate markers with low-positive predictive value and identifies promising markers for further validation.¹³

A phase 2 study following the above design is about to start at M.D. Anderson Cancer Center and will evaluate three potential genomic predictors for sensitivity to dasatinib in patients with metastatic breast cancer. Dasatinib is a multitargeted kinase inhibitor that may inhibit 19 separate kinases including BCR/ABL and several members of the SRC family and other kinases. The study will test in three separate parallel arms the predictive values of an SRC pathway activity signature, a cell line based genomic predictor, and a weighted index of all 19 target genes.

Molecular stratification is critical for correct interpretation of clinical trial results Lajos Pusztai, MD It is important to realize that the survival results from large randomized adjuvant chemotherapy trials for ER-positive breast cancer can be confusing and contradictory due to the differential activity of chemotherapy in different molecular subsets of ER-positive cancers. It is increasingly clear that not all ER-positive breast cancers benefit equally from adjuvant chemotherapy. In any particular adjuvant study, overall chemotherapy effects may or may not be significant among the ER-positive cancers depending on the proportion of the chemotherapy-sensitive subset. If the proportion of ER-positive and chemotherapy-sensitive cases is low than it is very difficult to observe any survival improvement in the ER-positive group. Molecular diagnostic tools now exist to gauge chemotherapy-sensitivity among ER-positive cancers. For example, the OncotypeDX high recurrence score group represents ER-positive cancers that derive the most benefit from chemotherapy, whereas the low-risk group derives little if any benefit. It is increasingly clear that not all ER-positive breast cancers benefit equally from adjuvant chemotherapy. Lajos Pusztai, MD It is logical to assume that an adjuvant chemotherapy trial that accrued and randomized by chance mostly OncotypeDX low-risk patients would yield a negative result, whereas another study that included many high-risk ER-positive cases could be positive even using the very same chemotherapy regimen. Randomization does not take care of this “referral bias.” Systematic differences in patient populations between similar trials may be caused by competing trials that are open at the same time or shifts in standard practice. For example, younger, high-grade ER-positive patients are preferentially offered participation in a study that compares more versus less adjuvant chemotherapy. Therefore, a parallel adjuvant study that compares adjuvant endocrine treatment with chemo-endocrine therapy will be depleted of the very patients who could benefit the most from chemotherapy. Routine use of trastuzumab will certainly remove a particularly chemotherapy-sensitive small subset of ER-positive patients from any future adjuvant chemotherapy trials. Proper molecular stratification is essential for correct interpretation of clinical trial results. Future studies will hopefully be designed with these molecular subsets in mind rather than for the entire breast cancer population. If we truly believe that breast cancer is not a single disease, than general breast cancer trials make no more sense than conducting a general cancer therapy study that is open for any type of solid tumor and presenting the results after stratification by hystological/anatomical diagnosis.”

Combination of Multiple Genomic Tests into a Single Assay

Combination of multiple genomic assays including prognostic and endocrine and chemotherapy response markers into a single assay could greatly enhance the cost-effectiveness of these tests. A study conducted by Pusztai and colleagues in collaboration with the European TRANSBIG research group illustrates the practical feasibility of this approach. The study was conducted in 198 stage I-II, node-negative breast cancer patients who received no systemic adjuvant therapy and 40 additional patients who received neoadjuvant T/FAC chemotherapy. Three distinct genomic predictors were used to evaluate each patient, including a 76-gene signature prognostic profile, a 30-gene chemotherapy predictor, and a 200-gene endocrine sensitivity index.18 Among 198 cases, 55 (28%) were assigned to the low-prognostic risk and 143 to the high-risk categories based on results from the 76-gene prognostic profile (Table 2). In the low-risk group, 21 patients (38%) were predicted to be highly sensitive to chemotherapy and 16 patients (29%) were predicted to be endocrine sensitive. Only two patients were predicted to be sensitive to both modalities. Among the 143 high-risk patients, 64 (45%) were predicted to be insensitive to chemotherapy and 109 (76%) were also predicted to have low sensitivity to endocrine therapy. Thirty-eight (26%) showed low sensitivity to both modalities. Similar observations were made among the patients who received neoadjuvant therapy, 14 patients (35%) were predicted to be at low risk and 26 patients (75%) were predicted to be at high risk for recurrence. Among the low-risk patients, pCR was achieved in four (28%) cases. In the high-risk group, four patients (15%) achieved pCR and another eight (30%) were predicted to be sensitive to endocrine therapy.

These results suggest that a small subset of patients at low (but not zero) risk for recurrence are highly sensitive to systemic therapies and that many patients at high risk for recurrence may be refractory to existing therapies. Simultaneous use of genomic predictors to determine risk of recurrence and likely sensitivity to various treatment modalities may prove useful in developing personalized treatment strategies. Individuals who are predicted not to do well with existing therapies represent ideal candidates for experimental treatments. These results also demonstrate that integrated “all-in-one” genomic tests are currently feasible technically and may provide clinical value through combining prognostic and predictive information. However, it is important to emphasize that combined prediction results are valuable only if the predictors included in the test are individually validated and accurate.

Ongoing Genomic Validation Studies

Simultaneous use of genomic predictors to determine risk of recurrence and likely sensitivity to various treatment modalities may prove useful in developing personalized treatment strategies.

While moderately accurate predictors or treatment response and outcomes currently exist, questions remain concerning the clinical usefulness of such predictors. Two large studies are currently evaluating the clinical utility of Oncotype DX and MammaPrint. The Microarray In Node-negative Disease may Avoid ChemoTherapy (MINDACT) study randomizes patients who have discrepant prognostic risk prediction results from the MammaPrint 70-gene signature and the Adjuvant Online (35% of all cases) to use either the results from the gene signature or the clinical model for treatment recommendation. The goal is to show that, by using the genomic predictor, 10% to 20% of women may be spared from adjuvant chemotherapy because of the greater accuracy of the genomic risk prediction without compromising 5-year distant relapse free.¹⁹ The study will include 6,000 patients. Accrual began in February 2007 and 93 patients have currently been enrolled (www.eortc.be/services/unit/mindact/MINDACT_websiteii.asp; accessed 01/17/08).

A second study, the Trial Assigning Individualized Options for Treatment[Rx] (TAILORx) is evaluating whether ER-positive patients in the intermediate recurrence score category determined by Oncotype DX benefit from adjuvant chemotherapy.²⁰ The study was started in May 2006. It includes 10,046 patients, 4,500 of whom will be randomized. As of December 8, 2007, 2,528 patients had been enrolled in the study (www.ctsu.org); keyword TAILORx. It will be many years before survival results will be available from this trial.

Recent Advances in Targeted Therapy for Breast Cancer

The advent of the “molecular era” in cancer treatment was marked by discovery of the Philadelphia (Ph) chromosome in 1960, the first chromosomal abnormality linked to a specific type of leukemia.^21,22 The Ph chromosome involves translocation of the ABL proto-oncogene normally found on chromosome 9 and the BCR gene on chromosome 22. It was demonstrated that the dysregulated ABL tyrosine kinase activity resulting from fusion protein expressed by the BCR-ABL gene was the pathogenic principle behind chronic myelogenous leukemia.²³ With a genetic target clearly identified, the process of drug development was allowed to proceed rationally with the goal of producing a drug that could block BCR-ABL.²³ The result of this work was imatinib, the first tyrosine kinase inhibitor approved for cancer treatment.

The numerous targeted agents in use and under development for various cancers illustrate the concept of molecular targeting in cancer therapy.

In line with the example of imatinib, trastuzumab, an antibody against the product of the HER2 oncogene, was approved for treatment of HER2-positive breast cancer. In this case, the clinical benefit conferred by the antibody appears to be limited to tumors with HER2 gene amplification. More recently, the next-generation tyrosine kinase inhibitor lapatinib has also been approved for treatment of HER2-positive breast cancer.²⁴ In addition, bevacizumab, a monoclonal antibody against vascular endothelial growth factor (VEGF), has been approved for the treatment of non-small cell lung cancer (NSCLC) and colorectal cancer and the tyrosine kinase inhibitor erlotinib, which binds epidermal growth factor receptor (EGFR), has been approved for the treatment of NSCLC.^25,26 The next-generation kinase inhibitors sunitinib, sorafenib, and temsirolimus, an inhibitor of the kinase mTOR, are indicated for the treatment of renal cell cancer (RCC).^27-29 Cetuximab, a chimeric monoclonal antibody against EGF, has been approved for the treatment of metastatic colorectal cancer, head and neck cancer, and panitumumab, a fully humanized monoclonal antibody against EGF, has been approved in colorectal cancer.^30-32

The numerous targeted agents in use and under development for various cancers illustrate the concept of molecular targeting in cancer therapy. Erlotinib owes its approval for NSCLC in good part to the discovery of EGFR mutations in lung cancer. Such mutations are present in 10% to 30% of patients with NSCLC and they may account for the majority of erlotinib activity in this disease.^33,34 Similarly, the efficacy of the kinase inhibitors sunitinib and sorafenib in RCC is predicated on their activity against the VEGF receptor, which is thought to play a central role in tumor angiogenesis in this cancer. The majority of renal cancers involve mutations that result in the inactivation of the von Hippel-Lindau tumor-suppressor gene (VHL). The VHL protein controls how much VEGF is produced by degrading the transcription factor hypoxia-inducible factor (HIF), which controls production of VEGF (Figure 3). With VHL inactivated in RCC, VEGF is overproduced and used for tumor maintenance.³⁵

Renal cancers are likely HIF-1a (and VEGF) dependent Figure 3. Control of hypoxia-inducible factor (HIF) by the gene product of the von Hippel-Lindau gene (pVHL). George DJ, Kaelin WG Jr., N Engl J Med. 2003;349:419. Copyright ® 2003 Massachusetts Medical Society. All rights reserved.

One of the most exciting new targeted agents in breast cancer is the tyrosine kinase inhibitor lapatinib, an ATP mimetic that reversibly inhibits both the EGFR and HER2 kinases. Lapatinib has predominant activity against HER2-overexpressing cancer cells as well as clinical activity against newly diagnosed HER2-positive metastatic cancers. It has demonstrated clinical activity against HER2-positive cancers that have progressed on trastuzumab and it was approved based on that indication.³⁶ In a phase 1 study, it was shown to be safe when given in combination with trastuzumab.³⁷ One potential advantage of lapatinib is that it is a small molecule. In a pivotal phase 3 trial, when lapatinib was added to capecitabine, there was a small reduction in risk for progression in the CNS (Figure 4).^38,39 It is possible that the small size of lapatinib allows it to more readily enter the CNS and may account for the difference in risk for CNS progression.

Brain Metastases as Site of Progression Figure 4. Phase 3 study of lapatinib and capecitabine in breast cancer: brain metastases as first site of progression. *P (Fisher’s exact, 2-sided)=.110 Cameron D, Casey M, Press M, et al. Breast Cancer Res Treat. Jan 11 2008. Geyer CE, Forster J, Lindquist D, et al. N Engl J Med. 2006;355(26):2733-2743

In an extension arm of a phase 2 study of lapatinib as a single agent in patients with recurrent brain metastases from HER2-positive breast cancer, patients who had progressive disease in the CNS and/or elsewhere were offered the combination of lapatinib and capecitabine.40 Of the initial 49 patients who received the combination, 10 (20%) experienced a >50% reduction in volume of CNS metastases. In addition, more than 40% of patients experienced a > 20% reduction in volume of CNS disease. These results in a small group of patients raise the question of whether this response in progressive disease is attributable to the addition of capecitabine or the combination of lapatinib and capecitabine. Findings from the study also have implications for the continuation of anti-HER2 therapy upon disease progression.

A number of recent and ongoing studies have focused on the molecular determinants of resistance to anti-HER2 therapies. Berns and colleagues recently published the results of a large-scale RNA interference screen to identify genes involved in trastuzumab resistance in breast cancer.⁴¹ They found that knocking out the locus of PTEN resulted in resistance to trastuzumab in breast cancer cell lines. In a review of a database of tumors from 55 breast cancer patients treated with trastuzumab, they found that tumors that had low PTEN expression and/or an oncogenic mutation of PI3 kinase had a shorter time to progression after trastuzumab therapy (Figure 5). With the combined analysis of PTEN and PIK3CA, twice as many patients with elevated risk for progression were identified compared with analysis of PTEN alone. The study concluded that PI3K pathway activation may represent a valuable biomarker to select breast cancer patients who are likely to escape the action of trastuzumab.

A functional genetic approach identifies the PI3K pathway as a major determinant of trastuzumab resistance in breast cancer Figure 5. Kaplan-Meier Survival Curves for Trastuzumab-Treated HER2-Positive Patients. Based on the PTEN scores and PIK3CA mutation data, patient groups were divided in activated PI3K pathway (PTEN low or oncogenic mutation in PIK3CA) and not-activated pathway (PTEN high + wild-type PIK3CA). Reprinted from Cancer Cell 12, Berns K, Horlings HM, Hennessy BT, et al., 395, 2007, with permission from Elsevier.

Results from this study raise the question of how best to inhibit trastuzumab-resistant HER2-dependent breast cancer. One option is lapatinib. However, tumors with PI3 kinase mutations and PTEN loss also appear not to be less sensitive to lapatinib compared to tumors with wild-type PI3 kinase and PTEN. Preliminary results from an ex vivo experiment in which PIK3CA mutants (p110a^E545K, P110^H1047R) are overexpressed in SKBR-3 breast cancer cells demonstrate that these cells become resistant to lapatinib.

Another option is the trastuzumab-DM1 HER2 antibody-drug conjugate currently under development for the treatment of HER2-positive breast cancer. The conjugate is designed to join the binding activity of trastuzumab with delivery capability of a potent antimicrotubule agent. The use of DM1, which binds tubulin potently in HER2-expressing cells, theoretically improves the therapeutic window for trastuzumab. In addition, the molecule used to link the two agents has been engineered to potentially improve exposure to the conjugate while minimizing exposure to free DM1. Krop and colleagues reported results from an ongoing phase 1 study evaluating the safety and pharmacokinetics of the conjugate.⁴² At the time of reporting, 19 patients who had progressed on a trastuzumab regimen received trastuzumab-DM1. At the maximum tolerated dose, drug-related adverse events grade ≥2, including ST-elevations, thrombocytopenia, fatigue, and anemia, occurred infrequently and were generally manageable. Objective tumor responses have been reported in four of 16 patients treated at or below the maximum tolerated dose of trastuzumab-DM1. In three patients, these responses have been confirmed and maintained after 1.7 to 5.5 months of treatment. Based on these promising results, phase 2 trials in advanced HER2-positive breast cancer are being initiated.

Continuation of trastuzumab in combination with chemotherapy after failure of trastuzumab is being investigated in the Trastuzumab treatment Beyond Progression (TBP) study. This study is evaluating whether continuation of trastuzumab in progressive disease results in improved time to progression. von Minckwitz and colleagues reported results from the TBP study, which was conducted in 152 women with HER2-positive, locally advanced or metastatic breast cancer who had developed progressive disease after receiving trastuzumab with or without chemotherapy as adjuvant or first-line treatment for metastatic disease.⁴³ The patients were randomized to either capecitabine or capecitabine with a continuation of trastuzumab. The primary endpoint for the study was time to progression. A planned interim analysis including 112 evaluable patients showed a time to progression (TTP) of 33 weeks for the trastuzumab continuation regimen compared with 24 weeks for the regimen without trastuzumab. The hazard ratio was 0.82 (95% CI, 0.53–1.26) in favor of the trastuzumab continuation regimen. Although the difference between the two treatment groups did not reach significance, interim results suggest that treatment with trastuzumab beyond progression in addition to capecitabine may be superior to capecitabine alone in women with HER2-positive advanced breast cancer that has progressed after initial treatment with trastuzumab. Final results from the TBP study are forthcoming.

Another drug being evaluated for trastuzumab-resistant HER-positive breast cancer is the irreversible EGFR/HER2 tyrosine kinase inhibitor HKI-272. Results from a phase 1 study showed that HKI-272 had acceptable tolerability and promising antitumor activity.⁴⁴ Burstein and colleagues reported preliminary results from an ongoing open-label phase 2 study in patients with HER2-positive advanced breast cancer.⁴⁵ The study has two arms: one including patients who previously had inadequate responses to trastuzumab and the other including patients who had no prior treatment with trastuzumab. At the time of reporting, preliminary data were available for 97 patients, 61 in the trastuzumab failure arm and 36 in the trastuzumab naïve arm. There were few grade 3/4 adverse events. The most common adverse events were diarrhea, nausea, fatigue, and vomiting, which were mostly of mild-to-moderate severity. At 23 weeks, 97 patients were free of progression. Among patients who had failed prior trastuzumab therapy, progression-free survival (PFS) was 16 weeks. For patients with no prior trastuzumab therapy, PFS was 33 weeks. These preliminary data suggest that HKI-272 may be useful in HER2-positive patients with trastuzumab-resistant disease.

One ongoing phase 2 study is evaluating the combination of the heat shock protein inhibitor (HSP90) tanespimycin and trastuzumab in patients with HER2-positive trastuzumab-refractory metastatic breast cancer.⁴⁶ Inhibition of HSP90 activity results in degradation of HSP90 client proteins including the HER2 receptor. In a previous phase 1 study, the combination of tanespimycin and trastuzumab resulted in an overall clinical benefit rate of 53%. At the time of reporting, 20 had been enrolled in the phase 2 study. Thirteen patients were evaluable for efficacy. Five patients had objective tumor responses in a population of heavily pretreated patients. Drug-related adverse events included fatigue (50%), diarrhea (38%), dizziness (31%), headache (25%), and dyspnea (19%). Grade 3 drug-related adverse events were seen in three patients and one patient withdrew from the study due to drug-related toxicity.

Other agents being investigated for usefulness in trastuzumab-resistant HER2-positive breast cancer are inhibitors of PI3K and AKT, insulin-like growth factor I receptor (IGF-IR), mTOR, ADAM metalloproteases (ADAM 10/17), and the SRC tyrosine kinase.^47-50

With many potential options existing for the treatment of trastuzumab-resistant HER2-positive breast cancer, what is the best strategy for determining the most effective option? One possibility is to do head-to-head comparisons in randomized phase 2 trials, in which each treatment is compared with chemotherapy plus trastuzumab (or with chemotherapy alone for the trastuzumab-DC1 conjugate) in a metastatic setting. Perhaps these trials would also have a third lapatinib arm. Such studies may not require a large number of patients in each arm to determine whether further evaluation is warranted. Patient selection for each study might benefit from what is already known about the sensitivity of molecular targets to the agents in question and focus on populations with HER2 overexpression.

Triple-Negative Breast Cancer

Breast cancer is increasingly emerging as a heterogeneous group of tumors, with distinct subtypes defined according to histopathologic features, genetic mutations, and gene-expression profiles.

Breast cancer is increasingly emerging as a heterogeneous group of tumors, with distinct subtypes defined according to histopathologic features, genetic mutations, and gene-expression profiles. Breast cancers that lack HER2 amplification as well as ER and PR expression are termed “triple-negative” tumors. Kreike and colleagues recently evaluated the gene expression profile and histopathology of 97 triple-negative breast cancer tumors in an effort to define triple-negative tumor subgroups and determine risk for developing progressive disease.⁵¹ Unsupervised hierarchical clustering with 7,770 significantly regulated genes was performed to clarify differences in gene expression among the sample of triple-negative tumors. Low HER2 and ER cluster expression as well as high basal cluster expression were evident. Fifty percent of the tumors were positive for p53 staining. All of triple-negative tumors were basal-like breast carcinomas, with five distinct subtypes. Multivariate analysis demonstrated that histopathologic factors including a large amount of lymphocytic infiltrate and absence of central fibrosis within tumors were independently associated with survival free of distant metastasis.

Results from two trials with EGFR antagonists in triple-negative breast cancer were recently reported. Carey and colleagues reported results from a randomized phase 2 study of cetuximab.⁵² The study randomized patients to one of two treatment arms: cetuximab alone with carboplatin added upon progression or cetuximab plus carboplatin throughout. Cetuximab alone was well-tolerated but had a low single agent response rate so failed criteria for ongoing study. Rapid progression in this population may have limited evaluation of efficacy. The second arm with the combination of cetuximab and carboplatin is ongoing. O’Shaughnessy and colleagues reported preliminary results from a randomized phase 2 study of the combination of irinotecan and carboplatin with or without cetuximab in patients with metastatic breast cancer.⁵³ The study randomized 163 patients to receive either irinotecan followed by carboplatin with or without cetuximab. In this preliminary analysis, the overall rate of response was 30% for the group that received only irinotecan and carboplatin versus 49% for the group that received irinotecan and carboplatin plus cetuximab. There were no differences in overall survival or progression-free survival between the two groups. The group receiving cetuximab had higher rates of toxicities than the group without. This preliminary analysis suggests that the addition of cetuximab to the combination of irinotecan and carboplatin does not improve treatment outcome and is associated with greater toxicity.

This preliminary analysis suggests that the addition of cetuximab to the combination of irinotecan and carboplatin does not improve treatment outcome and is associated with greater toxicity.

While results from studies of EFGR antagonists in triple-negative breast cancer have been overall negative—other studies have investigated inhibition of the SRC kinase. One preclinical study evaluated dasatinib, a small molecular kinase inhibitor of both SRC and ABL proteins, in 39 human breast cancer cell lines.⁵⁴ Eight out of 39 cell lines were highly sensitive to dasatinib and 10 cell lines had moderate sensitivity. The cell lines that were most sensitive to dasatinib were of the basal-type and/or those that had undergone an epithelial-to-mesenchymal transition. Breast cancer cell lines of the luminal subtype were largely resistant to dasatinib. These results were confirmed by another study using breast cancer cell lines to identify potential candidate molecular markers that might predict dasatinib sensitivity. The study found the triple-negative breast cancer subtype to be a potential marker for dasatinib sensitivity.⁵⁴ Based on these data, trials of dasatinib in triple-negative breast cancer have been initiated.⁵⁵

Key Abstracts SABCS 2007

The following abstracts were selected by Harold J. Burstein, MD, course director for this activity. These abstracts have been included in an attempt to provide a more comprehensive overview of current developments within breast cancer research.Additional comments by faculty are also provided to give practical perspectives on the implications of these abstracts.

ABSTRACT #48

ATLAS (Adjuvant Tamoxifen, Longer Against Shorter): international randomized trial of 10 versus 5 years of adjuvant tamoxifen among 11500 women preliminary results.

Peto R, Davies C, on Behalf of the ATLAS Collaboration.

Background: In estrogen receptor positive (ER+) early breast cancer, 5 years of tamoxifen substantially reduces the annual recurrence rate throughout the first decade (years 0-9). Despite this, appreciable risks of recurrence remain, and are persistent. Even with 5 years of tamoxifen, the annual recurrence risks for ER+ disease are comparably high during years 0-4, years 5-9 and years 10-14 (and perhaps beyond). It is not reliably known how 10 years of adjuvant tamoxifen compares with the current standard duration of tamoxifen, which is just 5 years.

Methods: During 1996-2005, ATLAS randomized 11500 women (59% ER+, 41% ER untested) in 420 hospitals in 38 countries who had completed ~5 years of adjuvant tamoxifen between continuing for another 5 years (i.e., to a total of 10 years) and control (i.e., stopping). The annual follow-up recorded information on compliance, hospital admission(s), breast cancer recurrence (including new contralateral disease), incidence of other new primary cancer, death and cause of death. Halfway through the trial treatment period, 83% of those allocated to continue and 4% of those allocated to stop were still taking adjuvant tamoxifen; <1% had switched to any other adjuvant hormonal treatment.

Results: During ~48000 woman-years of follow-up after randomization (mean 4.2 years per woman), the annual recurrence rate in each of the two treatment groups was approximately constant during and after the five-year trial treatment period (i.e., during years 5-9 and 10-14 after first starting tamoxifen). Some 1500 recurrences have been reported, ~1300 during years 5-9 but, in these preliminary results, only ~200 during years 10-14. Overall, the recurrence rate was significantly lower among those allocated to continue tamoxifen. There was no significant heterogeneity in this recurrence rate reduction with respect to ER status (ER+ or ER untested), time period (years 5-9 or 10-14), age or nodal status (at the time of diagnosis). There were ~700 deaths after recurrence (mostly from breast cancer) and ~500 deaths before recurrence (all from other causes). Although breast cancer mortality and overall mortality were lower among those allocated to continue, these differences were not statistically significant. There were no significant differences in mortality before recurrence, either overall or from particular causes.

Discussion: This large study shows that continuation of tamoxifen beyond the first 5 years reduces recurrence over the next few years, but further follow-up is needed to assess reliably the longer-term effects on recurrence and the net effects, if any, on mortality.

Harold J. Burstein, MD, PhD: Historically, 5 years of tamoxifen has been the standard treatment recommendation. Randomized trials from the NSABP, which looked at extended durations beyond 5 years, did not show clinical advantage to longer treatment durations. The ATLAS study was a large trial designed to examine tamoxifen duration limited to 5 years, versus longer treatment durations. It included over 11,000 women from around the world. The data presented at San Antonio Breast Cancer Symposium 2007 suggest that longer durations of tamoxifen appeared to have a favorable impact, lowering the risk of recurrence by around 10 to 15%. Unfortunately, the presentation did not include any toxicity analyses, and thus it is hard to weigh the potential trade-offs of longer therapy versus lower risk of recurrence. It is known that extending adjuvant endocrine therapy in postmenopausal women by offering an aromatase inhibitor (AI) after 5 years of tamoxifen can lower the risk of tumor recurrence. It is unclear how tamoxifen would stack up against an AI in such settings, though the relative risk reduction with tamoxifen in ATLAS seemed lower than that reported for letrozole in MA17. For postmenopausal women, switching from tamoxifen to an AI after 5 years seems a more appealing option than simply continuing tamoxifen based on the available data. However, for premenopausal women or women without access to AI therapy, it now appears that longer durations of tamoxifen may have small clinical advantages. It will be important to watch for longer follow-up from this trial and toxicity information as they emerge.

Lajos Pusztai, MD: This study showed statistically significant reduction in recurrence rate with extended tamoxifen therapy (>5 years) compared to observation (5 years of therapy only). This study adds to a growing body of literature that suggests that prolonged > 5 years of endocrine therapy is beneficial in ER-positive cancer. This squares well with clinical experience that indicates persistent risk of relapse well beyond 5-years in ER-positive cancers (unlike in ER-negative cancers where hazards drop to very low levels after 5 years).

The results from this study, if confirmed in the final analysis, may have limited implications in countries with large health care resources. Several high-quality randomized clinical trials showed the superiority of AI compared to tamoxifen and also proved that extended AI therapy reduces risk of recurrence compared to no further therapy after 5 years of tamoxifen. In the context of extended adjuvant therapy, AIs are the preferred drug. However, if the preliminary results from ATLAS are confirmed and particularly if survival benefit becomes apparent with longer follow up, extended tamoxifen therapy may be a cost-effective choice in nations with more restricted health care budgets. However, such cost-effectiveness analysis is yet to be performed.

Limitations: The monitoring and data collection of this trial was not presented in detail. The accuracy of collecting adverse events is particularly relevant for the final analysis of the study and to judge its clinical value. It is also concerning that 41% of study participants are ER-unknown. The lack of efficacy of tamoxifen in ER-negative patients is well-established and exposure of these patients to long-term and potentially toxic therapy is not warranted.

ABSTRACT #72

Three -Year follow-up of trastuzumab following adjuvant chemotherapy in node positive HER2-positive breast cancer patients: results of the PACS-04 trial.

Spielmann M, Roché H, Humblet Y, Delozier T, Bourgeois H, Serin D, Romieu G, Canon JL, Monnier A, Piot G, Maerevoet M, Orfeuvre H, Extra JM, Hardy AC, Martin AL, Kramar A, Genève J. Inst Gustave Roussy, France; Inst Claudius Ré gaud, France; UCL St-Luc, Belgium; Centre François Baclesse, France; CHU Poitiers, France; Inst Ste Catherine, Avignon, France; Centre Val dAurelle, France; CH ND Reine Fabiola, Belgium; CHG Montbelliard, France; CMC les Ormeaux, Le Havre, France; Clinique St Pierre, Ottignies, Belgium; CH Bourg en Bresse, France; Inst Curie, France; Cl Armoricaine St Brieuc, France; FNCLCC, France

Background: Following the PACS 01 trial, this randomised, multicentre, phase 3 trial was designed to evaluate the benefit of concomitant docetaxel (D) and epirubicin (E) versus anthracyclines, and the sequential use of trastuzumab (T) in the adjuvant treatment of node-positive (N+) early breast cancer (EBC).

Method: Women aged 65 years (yr) with N+ EBC were randomised initially to receive Arm A: 6 cycles (cy) of adjuvant 5-fluorouracil-epirubicin-cyclophosphamide (FEC100: F and C 500 mg/m², E 100 mg/m2), or Arm B: 6 cy of concomitant ED (E and D 75 mg/m²) every 3 weeks. Radiotherapy (RT) was performed after chemotherapy and hormonal therapy was prescribed to patients (pts) with hormone-receptor-positive tumours. As soon as HER2 status was available, pts with HER2+ (IHC3+ or IHC2+/FISH+) tumours were randomised to Arm C: observation only, or Arm D: 1 yr of T (8 mg/kg loading dose, 6 mg/kg 3qw). T was started after completion of RT for pts with normal cardiac function. The primary endpoint was 3-yr DFS for C and D arms. All survival times were calculated from first randomisation. To ensure a minimal power of 80% with a one sided =5% (HR=0.625), 520 pts were to be randomized to Arm C or D and 118 events were to be observed. Assuming a 20% HER2+ sub-population and a 10% drop-out rate before first T administration, it was estimated that a whole population of 3000 pts were to be recruited.

Results: 3010 pts (Arm A: n=1515, Arm B: n=1495), were randomized between 02/2001 and 08/2004. 528 HER2+ pts (18%) were randomised to Arm C (n=268) or Arm D (n=260). Baseline demographic and disease characteristics were well balanced between arms A and B as well as between C and D. 96% pts received 6 chemotherapy cy in arms A and B. 10% of pts in arm D did not receive T and 82% of the 233 pts in this Arm received T for more than 9 m, with a median cumulative dose of 109 mg/kg. Overall, 400 first events have been observed after a median follow-up of 36 months(m), but data are not mature for a comparative analysis between arms A and B. As of 30 April 2007, after a median follow-up of 40.5 m, 115 first events have been observed in HER2+ pts (18 locoregional relapses, 88 metastasis, 7 contralateral breast cancers, and 2 deaths) and the overall 3-yr DFS rate was 78%. Final efficacy and safety analysis will be presented for HER2+ pts.

Conclusion: This study will determine the potential benefit of combining ED in pts with N+ EBC and adding sequential T to FEC100 or ED75 in pts with HER2+ disease.

Harold J. Burstein, MD, PhD: The optimal chemotherapy/trastuzumab adjuvant regimen is not yet defined. A variety of regimens are widely employed worldwide, most built around anthracycline-based chemotherapy, followed by taxanes and trastuzumab. The PACS04 trial was a randomized study in which patients received anthracycline and taxane based chemotherapy, and were then randomized to sequential trastuzumab or not if the tumor was HER2 positive.

The results show a small advantage to adding trastuzumab after chemotherapy. In this respect, the study mirrors the HERA trial, which also gave chemotherapy first, followed by trastuzumab.

The Intergroup N9831 study compared sequential chemotherapy --> trastuzumab versus concurrent chemotherapy + trastuzumab. Unpublished data presented in 2005 suggest that the concurrent use of chemotherapy and trastuzumab yielded lower risk of recurrence. That practice remains the standard, and the data from PACS04, showing very small improvements with sequential chemo --> trastuzumab, should make the use of concurrent chemo/trastuzumab yet more the norm.

Pamela N. Munster, MD: The addition of trastuzumab to adjuvant therapy is now unequivocally proven to be beneficial; however, the optimal use of drugs and the timing are still under intense study. Emerging evidence suggests that the combination of anthracyclines with trastuzumab may have excessive risks, whereas the delay in trastuzumab until after chemotherapy results in loss of efficacy. In the PACS04 trial, the trastuzumab was started after completion of radiation therapy which may have resulted in a further delay. The PACS04 study, albeit a small study compare to the large Intergroup trials, lends further support to use of trastuzumab concurrent with a taxane after completing the anthracycline-containing part of the treatment.

ABSTRACT #4056

Trastuzumab treatment beyond progression in patients with HER-2 positive metastatic breast cancer the TBP study (GBG 26/BIG 3-05).

von Minckwitz G, Vogel P, Schmidt M, Eidtmann H, Cufer T, de Jongh F, Maartense E, Zielinski C, Andersson M, Stein R, Neklju-dova V, Loibl S. University Hospital Frankfurt, Frankfurt, Germany; German Breast Group, Neu-Isenburg, Germany; Klinik f r Gyn kologie und Gyn kologische Onkologie, Wiesbaden, Germany; University Hospital Mainz, Mainz, Germany; Studienzentrale Gyn kologische Onkologie (SGO) Kiel, Kiel, Germany; Institute of Oncology Ljubljana, Ljubljana, Slovenia; Ikazia Zickenhuis, Rotterdam, Netherlands; Reinier de Graaf Gasthuies, Delft, Netherlands; University Hospital and Cancer Centre, Wien, Austria; Rigshospitalet University Hospital, Kopenhagen, Denmark; University College London Hospital, London, United Kingdom

Background: Trastuzumab has proven efficacy in patients with HER-2 positive metastatic breast cancer. There is uncertainty, if continuation of trastuzumab beyond progression (TBP) improves time to progression (TTP) of the next therapeutic step.

Patients and methods: Women with HER-2 positive, locally advanced or metastatic breast cancer that had progressed dur-ing or after a treatment with trastuzumab with or without chemotherapy as adjuvant or 1st-line treatment were randomly assigned to receive either capecitabine (X) 2500 mg/m2 on days 1-14, q21 or the same capecitabine treatment simultaneously to a continuation of trastuzumab (XH) 6 mg/kg body weight every 3 weeks. Trastuzumab-free interval before study participation had to be less than 6 weeks. The primary end point was TTP.

Results: Between 01/04 and 05/07 152 of 482 planned pts (77 in X and 75 in XH) were randomized after pre-treatment with a taxane/trastuzumab combination as 1st-line therapy (105 pts), trastuzumab alone or with a non-taxane containing chemotherapy as 1st-line treatment (43 pts), taxane or trastuzumab as part of adjuvant treatment (4 pts). Due to slow accrual the trial was closed end of May 2007 on advice of the IDMC. A pre-planned interim analysis including 119 patients (112 evaluable) revealed a TTP of 24 and 33 weeks for X and XH, respectively, P=0.178 (one-sided log-rank test). The hazard ratio was 0.82 (95% confidence interval, 0.53 to 1.26) in favour of XH, with 42 events in the combination group and 40 events in the monotherapy group. No difference in serious adverse events was observed (29 X, 20 XH). 1 myocardial infarct and 1 LVEF decrease were observed during XH.

Conclusion: Treatment with trastuzumab beyond progression in addition to capecitabine shows a trend to be superior to capecitabine alone in women with HER2-neu positive advanced breast cancer that has progressed after 1st line trastuzumab treatment. The difference was non-significant at this stage of analysis. Final results on all randomized patients will be reported.

Harold J. Burstein, MD, PhD: The question of what to do after tumor progression on trastuzumab has been a challenging one since the development of the drug. Because trastuzumab is generally well tolerated, and because it was thought that trastuzumab might potentiate the effects of subsequent lines of chemotherapy, American oncologists adopted the habit of continuing trastuzumab beyond treatment progression.

Lapatinib, the orally available dual kinase inhibitor, was FDA approved for trastuzumab-resistant, HER2-positive breast cancer. In a randomized trial of patients progressing on trastuzumab, the combination of capecitabine + trastuzumab yielded longer time to tumor progression and higher response rates than did capecitabine alone. A similar study was ongoing at the same time in Europe, looking at capecitabine alone versus capecitabine plus trastuzumab for patients with tumors progressing after initial trastuzumab treatment. This trial was closed when the lapatinib result became available. The work by von Minckwitz shown at SABCS 2007 suggests that ongoing trastuzumab does in fact potentiate the effects of the next line of chemotherapy, improving both response rate and time to tumor progression. It is not clear which strategy—continuing trastuzumab and switching chemotherapy agents, or switching trastuzumab to lapatinib and switching chemotherapy agents—would be superior, and it is possible that in the future, using both anti-HER2 agents could be contemplated. For the time being, it is clear that multiple lines of anti-HER2 therapy can yield clinical advantages to patients. In this respect, anti-HER2 therapy is similar to anti-estrogen therapy for ER-positive breast cancer, with multiple available agents, and demonstrable clinical benefit for multiple lines of treatment.

This preliminary analysis suggests that the addition of cetuximab to the combination of irinotecan and carboplatin does not improve treatment outcome and is associated with greater toxicity.

Pamela N. Munster, MD: This abstract presented by von Minckwitz set out to answer an important question. Should targeted therapy directed against HER2 continue after failing a combination of HER2 targeting and chemotherapy? In this case the HER2 targeting therapy was trastuzumab. The question was answered in part with the approval of lapatinib in combination with capecitabine, which also possibly led to poor accrual to this trial. It appears that after progression on trastuzumab/chemotherapy, there is a clear benefit for patients with HER2-positive tumors in adding the HER2 targeting kinase inhibitor to capecitabine, or as suggested in this abstract to change the chemotherapeutic agents while maintaining the HER2 targeting monoclonal antibody. This abstract further suggests a need and potential benefit to study HER2 targeting strategies either alone or in combination with other modalities.

Adjuvant Chemotherapy for Breast Cancer

Rates of Death from Breast Cancer Figure 6. Estimated and actual rates of death from breast cancer among women 30 to 79 years of age from 1975 to 2000 (A) and under hypothetical assumptions about the use of screening mammography and adjuvant treatment (B). Berry, D et al. N Engl J Med. 353:1784, 2005. Copyright ® 2005 Massachusetts Medical Society. All rights reserved.

Advances in early detection and treatment of breast cancer have resulted in dramatic decreases in deaths from the disease. The impact of these interventions was assessed in a recent study by the Cancer Intervention and Surveillance Modeling Network (CISNET). Seven independent statistical models were used to examine the relationship between screening and adjuvant treatment and breast cancer incidence and mortality. Figure 6 shows estimates of rates of mortality between 1975 and 2000 from the seven models, comparing these to actual rates of mortality in the United States. All of the models predicted similar reductions in deaths from the combined approach of screening and treatment. In the absence of screening and adjuvant treatment, estimated rates of mortality would have increased by 30% between 1975 and 2000 (Figure 6). The combination of screening and treatment accounted for an estimated 25% to 38% drop in mortality over this period.⁵⁶

The EBCTCG overview clearly demonstrated the superiority of anthracycline-based regimens over CMF as adjuvant therapy.

Although there is little doubt of the role of adjuvant therapy in reducing breast cancer mortality, important questions remain concerning the use of such therapy. Various studies have sought to clarify precisely which breast cancer patients will benefit from adjuvant therapy. Other studies have examined the role of agents including anthracyclines, taxanes, and newer targeted drugs in adjuvant treatment. Additionally, studies have tried to determine whether the scheduling of chemotherapy makes a difference in outcomes and whether it is possible to accurately predict responses to various agents.

The Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) conducted meta-analyses of 195 randomized trials of adjuvant therapies conducted since 1995 and reported effects of chemotherapies and hormonal therapies on recurrence and 10- and 15-year survival.⁵⁷ The study found that regimens of single-agent chemotherapy significantly reduced rates of recurrence (P=.001) and that regimens of polychemotherapy resulted in significant reductions in both rates of recurrence and mortality (recurrence rate ratio: 0.77; death rate ratio: 0.83; P<.00001 for both). For both types of regimens, younger patients tended to derive the greatest benefits, both in terms of recurrence and mortality. However, across all age groups, polychemotherapy had a significantly greater favorable effect on recurrence and mortality than single-agent regimens. Meta-analysis of studies comparing anthracycline-based regimens with the classic chemotherapy regimen CMF (cyclophosphamide, methotrexate, fluorouracil) involving 14,000 breast cancer patients found that anthracyclines offered a highly significant advantage over CMF in terms of both recurrence (recurrence rate ratio: 0.89; P=.001) and mortality (death rate ratio: 0.84; P<.00001). Younger and older women appeared to derive comparable benefit from anthracycline-based regimens.

The EBCTCG overview clearly demonstrated the superiority of anthracycline-based regimens over CMF as adjuvant therapy. However, questions remain concerning patient selection for such therapy and whether markers (e.g., HER2, topoisomerase II-alpha [TOP2A]) might predict optimal responses.

Pritchard and colleagues examined whether HER2 overexpression was associated with responsiveness to anthracycline-containing chemotherapy in a study of 639 tumor specimens from 710 patients with node-positive breast cancer.58 Patients had received adjuvant therapy with either CMF or cyclophosphamide, epirubicin, and fluorouracil (CEF). Patients with HER2 overexpression on fluorescence-in-situ hybridization (FISH) had a poor prognosis regardless of which type of treatment they received. However, the anthracycline-based regimen (CEF) resulted in superior rates of relapse-free survival (relapse-free survival) compared with CMF (HR, 0.52; 95% CI, 0.34 to 0.80; P=.003) and overall survival (HR, 0.65; 95% CI, 0.42 to 1.02; P=.06). For patients without HER2 overexpression, there was no advantage for either treatment regimen in terms of relapse-free survival or overall survival. The authors conjectured that the relationship between HER2 overexpression and responsiveness to anthracycline may be related to topoisomerase II alpha. Anthracyclines are inhibitors of topoisomerase, and HER2 and TOP2A are located in close proximity on chromosome 17. Measurement of TOP2A or changes in TOP2A in tumors may prove useful as predictors of response to anthracycline-based adjuvant therapy.⁵⁸

The prognostic and predictive value of TOP2A was evaluated in the National Cancer Institute of Canada (NCIC) Clinical Trials Group (CTG) Trial MA5 comparing CEF and CMF in premenopausal patients with node-positive breast cancer.59 The study was conducted in 710 women who were randomized to CEF or CMF. For analysis of TOP2A, tissue samples were taken from 447 patients. TOP2A measurements were made using FISH, and tumors were categorized into three groups according to whether TOP2A was deleted (n=27 [6.1%]), amplified (n=48 [10.8%]), or normal (n=368 [83.2%]). TOP2A status was demonstrated to be a significant predictor of benefit from anthracycline-based therapy. In an adjusted analysis, patients with TOP2A alterations who received CEF had significantly greater disease-free survival than those who received CMF.

Despite the promise of TOP2A as a predictor of response to adjuvant therapy, there are some important limitations to currently available data. Studies using FISH and immunohistochemical (IHC) staining have not been consistently concordant, and IHC studies need to consider the intracellular localization of TOP2A. While TOP2A overexpression or TOP2A gene amplification or deletion may prove to be useful in choosing between CMF and an anthracycline-based regimen, additional studies are needed if these assays are to be used in other clinical contexts.⁶⁰

Comparison of First Generation Adjuvant Taxane Trials Figure 7. Relative Differences in DFS and OS at 5 Years. Reprinted with permission from Budd GT

The first-generation taxanes, paclitaxel and docetaxel, have played an important role in adjuvant therapy for breast cancer. Although results from major randomized trials of these agents demonstrate discrepancies between rates of 5-year disease-free survival and overall survival (Figure 7), the adjunction of taxanes has been shown to significantly improve both disease-free survival and overall survival. A pooled analysis of phase 3 trials of adjuvant paclitaxel and docetaxel involving 15,500 patients demonstrated a consistent though small (2% to 4%) benefit in favor of these drugs in terms of both disease-free survival and overall survival across all subpopulations. The absolute benefit from these drugs in this setting is similar to that seen with anthracyclines in the EBCTCG meta-analysis.⁶¹

Studies are seeking to clarify important questions that remain concerning the use of taxanes, including whether ER and HER2 markers are predictive of response and whether these markers can be used as the basis for choosing between paclitaxel and docetaxel.

An upcoming Oxford Overview by the EBCTCG will examine the benefit that taxanes provide in the adjuvant setting in both node-positive and node-negative patients. However, another recent review of results from six randomized phase 3 studies evaluating the benefit of adding a taxane to an anthracycline-based regimen either concomitantly or sequentially (BGIRG 001, ECOG 2197, PACS 01, GEICAM 9906, CALGB 9344, NSABP B28) found that the taxane arm in five of these studies had significantly better outcomes in terms of disease-free survival (GEICAM 9906, NSABP B28) or both disease-free survival and overall survival (BGIRG 001, PACS 01, CALGB 9344).⁶² The superiority of the taxane arms in these studies was demonstrated in subgroup analyses, including number of involved lymph nodes, ER status, and HER2 status. Another study (USO 9735) evaluating the substitution of an anthracycline with a taxane found that disease-free survival improved in the taxane arm.⁶²

Studies are seeking to clarify important questions that remain concerning the use of taxanes, including whether ER and HER2 markers are predictive of response and whether these markers can be used as the basis for choosing between paclitaxel and docetaxel. Three studies of adjuvant taxane therapy (CALGB 9344, CALGB 9741, CALGB 8541) (Table 3) have examined the effect of ER status on disease-free survival and overall survival. The average hazard reductions in terms of both disease-free survival and overall survival appear to be considerably lower for patients with ER-positive disease than those with ER-negative disease. However, results from other studies suggest that paclitaxel and docetaxel have comparable efficacy in patients with ER-positive disease.

In the CALGB 9344 study, Hayes and colleagues examined whether HER2 status would predict outcomes with adjuvant paclitaxel given after anthracycline-based chemotherapy.⁶³ The study was conducted in 1,500 node-positive breast cancer patients randomized to either doxorubicin (at one of three dose levels) plus cyclophosphamide followed by either paclitaxel or observation. Tumor biopsies were taken from 1,322 of the patients and analyzed for HER2 expression via antibody assays and for HER2 amplification via FISH. The study demonstrated that patients with tumors that were either HER2-positive or ER-negative derived a significant benefit from adjuvant paclitaxel. Multivariate analysis showed the interaction between the addition of paclitaxel and HER2 positivity to be associated with hazard ratios for recurrence and death of 0.59 (P=.01) and 0.57 (P=.01), respectively. Figure 8 shows Kaplan-Meier curves for disease-free survival according to ER status and HER2 expression. The addition of paclitaxel was associated with significant advantages in disease-free survival for patients who were HER2-positive regardless of ER status. Additionally, patients who were both ER-negative and HER2-negative also benefited significantly from the addition of taxane therapy.⁶³

HER2 Status with and without Paclitaxel Treatment Figure 8. DFS in Patients Treated With or Without Paclitaxel, According to HER2 Status. Copyright ® 2007 Massachusetts Medical Society. All rights reserved.

Randomization and Dosing-Schedule for Study C9741 Figure 9. Study sought to determine the most beneficial schedule by comparing and randomizing 2,005 patients to one of four dosing schedules. Citron M, et al. Breast Cancer Res Treat 2002;76(suppl 1):S32. (abstr 15)

With the advantages of adjuvant combinations of taxane and anthracycline-based therapies demonstrated by studies such as CALGB 9344, questions remain concerning the optimal scheduling of these combinations. Study C9741 sought to determine the most beneficial schedule by comparing and randomizing 2,005 patients to one of four dosing schedules (Figure 9): (1) a sequential schedule, (2) a dose-dense sequential schedule, (3) a concurrent schedule, and (4) a dose-dense concurrent schedule.^64,65

OS by Hormone Receptor and HER2 Status Figure 10. High-dose chemotherapy versus low-dose chemotherapy as adjuvant therapy. Reprinted with permission from Berry DA, Ueno NT, Johnson MM, et al. J Clin Oncol. Apr 15, 2003; 21(8):1431-1439.

With a median follow-up of 3 years, results showed that the dose-dense schedules were associated with significantly longer disease-free survival compared with the every-3-week concurrent and sequential schedules (hazard ratio: 0.74, P=.01). Although there was no difference in disease-free survival by dosing sequence, there was a significant difference in disease-free survival by dosing density (Figure 10).⁶⁵

While TOP2A overexpression or TOP2A gene amplification or deletion may prove to be useful in choosing between CMF and an anthracycline-based regimen, additional studies are needed if these assays are to be used in other clinical contexts.

A recent meta-analysis of data from 15 randomized trials of adjuvant therapies in breast cancer compared regimens of high-dose chemotherapy plus autologous stem-cell support with standard dose chemotherapy.⁶⁶ The trials involved in this analysis included a total of 6,210 patients, 3,118 of whom had received the high-dose regimen and 3,092 of whom had received the standard-dose regimen. The two treatment regimens were compared with respect to relapse-free survival and overall survival, adjusting for age, trial, and ER status and the median follow-up was 6 years. High-dose chemotherapy provided only a modest benefit over low-dose chemotherapy in relapse-free survival and little or no benefit in overall survival. In subgroup analyses, the group of patients who were hormone receptor-negative and HER2-negative and received the high-dose regimen had a significant advantage in overall survival over their low-dose counterparts (Figure 10). In each of the other subgroups where patients were positive for hormone receptors or HER2 or both, high- and low-dose regimens resulted in comparable overall survival. So high-dose chemotherapy appeared to offer little benefit for most of the patient subgroups, and perhaps for all subgroups, across the 15 trials. Although subgroup analyses are always difficult to interpret, patients with triple-negative disease may have derived some benefit in terms of overall survival.

Predicting Risk of Recurrence After Adjuvant Therapies in ER-positive Breast Cancer

In a recent study, Paik and colleagues evaluated the magnitude of benefit from adjuvant chemotherapy as a function of the Oncotype DX 21-gene Recurrence Score (RS) assay in a subset of the NSABP B20 randomized trial.⁶⁷ The biomarker study retrieved tumor specimens from 430 patients randomized to tamoxifen alone or tamoxifen plus chemotherapy and examined recurrence rates and benefit from chemotherapy by RS category. Patients who were identified as high-risk derived significantly more benefit from chemotherapy than did those in the RS intermediate- and low-risk categories. The addition of chemotherapy to tamoxifen in the high-risk patient group resulted in an improvement in freedom from distant recurrences from 60% to 88%.⁶⁸ The study suggested that the Oncotype DX assay was successful in predicting the magnitude of benefit from chemotherapy in the various subgroups of ER-positive patients. However, this analysis included some of the same patients who were included in the development and optimization of the assay and this can bias the results toward better performance.

Results from an analysis of the prognostic and predictive value of the Oncotype DX 21-gene RS assay in the SWOG 8814 (TBCI 0100) trial were recently presented and suggested that the Recurrence Score assay may be useful in determining patients with node-positive postmenopausal disease who will benefit from adjuvant anthracycline therapy added to hormonal therapy.⁶⁹ The SWOG 8814 phase 3 trial evaluated adjuvant treatment in postmenopausal, node-positive, ER-positive breast cancer patients. The study randomized 1477 patients to one of three tamoxifen regimens: (1) adjuvant treatment with 5 years of tamoxifen only (n=361), (2) CAF cyclophosphamide/doxorubicin/fluorouracil) plus concurrent tamoxifen (n=550), (3) CAF followed by tamoxifen (n=566). Study endpoints were disease-free survival and overall survival. The study demonstrated superior disease-free survival and overall survival for the group receiving CAF followed by tamoxifen.⁷⁰ A retrospective biomarker subset analysis of this study was performed by applying Oncotype DX assay to 367 patients randomized to the tamoxifen alone or the sequential tamoxifen CAF treatment arms. The 21-gene RS was prognostic for both disease-free survival and overall survival in the tamoxifen arm, demonstrating significant differences in survival outcomes among high-, intermediate-, and low-risk groups. However, the absolute recurrence rate (including contralateral breast cancer and ipsilateral locoregional recurrences) was 40% in the low-risk group. This rate is higher than most patients and physicians feel comfortable with. Also, the rate varies from the disease-free survival rate of ER-positive, node-negative patients with similar low RS. The RS assay was also predictive of therapeutic benefit of adding CAF to tamoxifen, demonstrating significant benefit in only high-risk patients. The absolute improvement due to chemotherapy was 4% in the low RS category and this was not statistically significant. However, the total number of patients in the low RS category was 146, which makes this subset analysis underpowered to rule out small but real benefit from adjuvant chemotherapy in this group. The significance of the RS assay predictive effect was retained in Cox models adjusted for covariates including age, race, tumor size, PR status, grade, and HER2 status. However, the significance was lost when the ER Allred score was added to the model.⁶⁹

Other studies examined the prognostic utility of Oncotype DX in node-negative and node-positive (1-3 nodes) patients who received adjuvant chemotherapy and hormonal therapy. Goldstein and colleagues conducted an analysis of Intergroup trial E2197 to evaluate the prognostic utility of Oncotype DX compared with Adjuvant Online (www.adjuvantonline.com).⁷¹ Archived tissue samples were retrieved from 465 patients with hormone receptor (HR)-positive disease who participated in the E2197 study. This study (N=2885) compared adjuvant doxorubicin plus cyclophosphamide (AC) with docetaxel plus cyclophosphamide (AT), followed by tamoxifen in each treatment arm. Among these patients, 366 had experienced a recurrence and 99 had no recurrence, the cases were selected by the investigators following a case-control study design. Oncotype DX RS assay was a significant predictor of recurrence (local and distant), in both node-negative (P=.0007) and node-positive (P=.0004) disease. Low RS was associated with 3% and 8% recurrence rates in the 0-1 and 2-3 positive lymph node categories at a median follow-up of 76 months. The RS provided additional prognostic information to the clinical variables evaluated by Adjuvant Online.

A limitation of the study is that all patients received chemotherapy and therefore it remains uncertain to what extent chemotherapy contributed to the good survival of the node-positive low RS group. Similarly, longer follow-up may be needed to truly compare the genomic prediction results with that of Adjuvant Online that was optimized for predicting 10-year survival outcome. This is important because different clinical and molecular factors may predict for early (5 year) and late relapse (≥5 years).

In aggregate, these results support the prognostic value of Oncotype DX in ER-positive cancers. The data also suggest that nodal status caries additional prognostic value. The true risk of relapse of patients with node-positive ER-positive low RS category treated with endocrine therapy alone remains uncertain. The SWOG 8814 study suggests a high rate of breast cancer related events (including local recurrence and second primary cancers as well as distant metastasis).

Update on Endocrine Therapy

The standard option for adjuvant endocrine therapy in premenopausal women is tamoxifen continued for 5 years. However, questions concerning the optimal duration of tamoxifen in premenopausal women exist. In postmenopausal women, the standard option is aromatase inhibitor (AI) therapy, either the up front, sequential, or extended use. Results from recent studies address some of the questions concerning the use of endocrine therapy in breast cancer.

Recent Results From Studies of Tamoxifen

Early results from the Adjuvant Tamoxifen Longer Against Shorter (ATLAS) trial, a major international study of adjuvant tamoxifen, suggest that the therapeutic benefit of tamoxifen therapy may not be limited to 5 years, as had previously been indicated by the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-14 study.⁷² NSABP B-14 had previously demonstrated that the therapeutic benefit derived from 5 years of tamoxifen therapy was not improved by the extension of tamoxifen to 10 years of treatment.⁷³ In the ATLAS trial, patients with a diagnosis of early stage breast cancer were randomized to further tamoxifen or no treatment after having completed 5 years of tamoxifen. The study enrolled 11,500 patients in 38 countries. A possible limitation of the study is that ER-testing was performed only in the 59% of patients that tested ER-positive, while 41% remained untested, resulting in an estimation of 90% of patients being ER-positive. Adherence to the regimen was believed to be approximately 80%. The mean follow-up was 4.2 years.

Results indicate that continuing tamoxifen therapy for an additional 5 years confers about a 12% relative reduction in risk of recurrence compared with tamoxifen discontinued after 5 years (HR: 0.88, P=.05) for years 5 to 9. Hazard ratios for recurrence for continued tamoxifen versus discontinued treatment were 1.0 for the first year after randomization, 0.90 for years 2 to 4, and 0.72 for year 5 and beyond. There were no significant differences in breast cancer-specific survival and overall survival between the two groups. Overall, there have been 739 recurrences for the group of patients randomized to continue treatment versus 835 recurrences for the group that stopped treatment. Of these recurrences, 221 were observed between years 10 and 14 of the study. Among patients who continued to receive tamoxifen for a second 5-year period, there has been a carry-over effect with an additional reduction in risk of 22%. Of those, 221 occurred among women in years 10 through 14 of the study, 96 in the tamoxifen continuation group, and 115 in the group that received tamoxifen for 5 years.⁷³ These findings differ from those of the smaller NSABP B-14 trial, which had found that use of tamoxifen beyond 5 years might be worse than stopping after 5 years. Comparison of results for risk of recurrence from ATLAS with EBCTG data demonstrate the extent to which ATLAS may change perceptions of the usefulness of adjuvant tamoxifen beyond 5 years (Table 4). The size of the ATLAS study, which is the largest ever in adjuvant therapy in breast cancer, lends weight to these findings. Additionally, the unclear ER status of the population in ATLAS may mean that efficacy is being underestimated. However, no data on toxicities were presented, impeding a thorough risk to benefit assessment. These findings are significant because adjuvant aromatase inhibitor therapy has become accepted as the best means of prevention of recurrence. However, tamoxifen therapy is significantly less expensive and, based on results from ATLAS, tamoxifen may have a longer therapeutic benefit than previously thought. In addition, these data may be useful in determining the length of therapy with tamoxifen in patients who cannot tolerate aromatase inhibitor therapy.⁹ The Adjuvant Tamoxifen Treatment–Offer More? (aTTom) trial, another large-scale study of adjuvant tamoxifen, has recently finished patient accrual and may shed further light on the question of optimal duration of adjuvant tamoxifen therapy.

Results from the ATLAS study must also be seen in the context of data from the MA-17 trial, in which the aromatase inhibitor letrozole was given to patients who had completed 5 years of tamoxifen. Letrozole was well-tolerated and reduced recurrence risk by 42% and risk of distant metastases by 40% versus placebo. Because of the significant advantage in disease-free survival provided by letrozole, the study was unblinded early. Patients who elected to receive letrozole after unblinding experienced significant improvements in disease-free survival. The magnitude of benefit from letrozole in prevention of relapse after 5 years of tamoxifen makes a strong case for use of aromatase inhibitor therapy in this setting.⁷⁴

The association of tamoxifen with increased incidence of uterine abnormalities (e.g., uterine cancer, sarcoma, endometrial hyperplasia, fibroids) is widely recognized. These effects are thought to be linked to the partial agonistic activity that tamoxifen exerts in the uterus. The Intergroup Exemestane Study (IES) is evaluating the effect of tamoxifen and the steroidal aromatase inhibitor exemestane on endometrial status in postmenopausal patients with early breast cancer who have been free of disease after 2 to 3 years of tamoxifen treatment. Patients (N=4724) were randomized to continued tamoxifen or exemestane treatment to complete 5 years of adjuvant therapy. During treatment, endometrial thickness remained stable in the tamoxifen group. Switching to exemestane resulted in rapid and significant improvements in endometrial thickness and uterine volume. At 6 months, the change from baseline was -1.9 mm (P=.003). At 2 years, there was a significant difference in the percentage of patients in the tamoxifen and exemestane groups with abnormal endometrial thickness (35.5% versus 61.8%, P=.004). Following treatment, endometrial thickness and uterine volume decreased in the tamoxifen group, suggesting that improvement in endometrial status resulted from withdrawal of tamoxifen rather than a protective effect of exemestane (Table 5).

Recent reports have indicated that polymorphism in genes associated with metabolism, including the CYP2D6 gene, may impact tamoxifen efficacy and tolerability. The CYD2D6 enzyme metabolizes tamoxifen to endoxifen, which is most likely responsible for much of the effect of tamoxifen. Approximately 8% of Caucasians are poor metabolizers of tamoxifen and will have poor outcomes if treated with the drug. The same mechanism may affect responses and side effects with aromatase inhibitors. Cuzick and colleagues evaluated the occurrence of hot flushes in a retrospective, exploratory analysis of results from the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial.75 The analysis identified all patients who reported the side effect associated with either tamoxifen or anastrozole during the first 3-month follow-up visit. Hot flushes were reported in 35% of the women at 3 months (36% anastrozole versus 41% tamoxifen). Patients who experienced hot flushes had a 3.6% lower risk of recurrence than those who did not (A: HR 0.66 (P<.001), T: 0.77 (P=.006). This significant difference was seen in both treatment arms. These data suggest that, for both treatments, effectiveness is associated with occurrence of hot flushes. This symptom may be an indirect measure of the degree of suppression of estrogen or ER blockade achieved by these treatments.

Recent Studies of Anastrozole

In agreement with the MA-17 trial findings, results from the ATAC study also demonstrated a therapeutic advantage with aromatase inhibitor therapy over tamoxifen, while dispelling some of the concerns with adverse effects associated with this class. Forbes and colleagues presented results from the ATAC study with median follow-up of 100 months.⁷⁶ The follow-up demonstrated the continued superior efficacy of the aromatase inhibitor anastrozole and no excess risk for fracture compared with tamoxifen upon completion of therapy. Earlier follow-up had shown that anastrozole was significantly more effective than tamoxifen in prevention of recurrences with better tolerability but with a higher risk for fractures.⁷⁷ This large, randomized, double-blind phase 3 study of 5-year adjuvant hormonal treatment for early breast cancer randomized 3125 postmenopausal women to anastrozole and 3116 to tamoxifen. Anastrozole resulted in a significantly higher rate of DSF (primary endpoint) versus tamoxifen (HR: 0.85; 95% CI 0.76, 0.94; P=.003). There was also a significant advantage in favor of anastrozole with respect to time to recurrence (TTR), time to distant recurrence, and new contralateral breast cancer (Table 6). Over time, there was an increase in the absolute difference in TTR between the two arms: 2.7% at 5 years and 4% at 9 years. Rates of overall survival were comparable. Following completion of therapy, anastrozole and tamoxifen were associated with comparable rates of fractures.⁷⁶

The magnitude of benefit from letrozole in prevention of relapse after 5 years of tamoxifen makes a strong case for use of aromatase inhibitor therapy in this setting.

Another analysis of data from ATAC focused on risk factors for joint symptoms. Such symptoms are a recognized side effect of aromatase inhibitor therapy and are associated with postmenopausal status and low estrogen levels. However, tamoxifen therapy appears to have minimal impact on the development of joint symptoms. The analysis examined risk factors that had an influence on the development of joint symptoms and assessed whether there was an association between these symptoms and endocrine treatment.⁷⁸ With a median follow-up of 68 months, 2,011 joint symptoms were observed. Rates of joint symptoms were higher in the anastrozole group (35.6%) than in the tamoxifen group (29.4%) (OR=1.32 [1.19-1.47]). In patients who received hormone replacement therapy (HRT) before the study, the rate of joint symptoms during the study was higher than for those who received no HRT. Joint symptoms were significantly more common in patients who received chemotherapy as part of treatment versus those without chemotherapy (OR=1.31 [1.15-1.48]). Patients with tumors that were hormone receptor negative had significantly fewer joint symptoms than those who were hormone receptor positive (OR=0.67 [0.55-0.83]). Other significant positive factors for development of joint symptoms included geographical origin in North America (United States and Canada), increased body weight, and cigarette smoking.⁷⁸

Updated results from ATAC also included some previously unreported toxicities, including retinal hemorrhages associated with anastrozole therapy.⁷⁹ The authors speculate that this finding may be explained by the recognized association of aromatase inhibitors with compromised systemic vascular integrity. Additionally, the retina itself may be directly impacted by depletion of estrogen due to the location of ER in the retina. Risk for retinal hemorrhages was evaluated by obtaining retinal fundus photographs for 35 patients who received anastrozole, 38 amenorrheic patients who received tamoxifen, and 38 amenorrheic control subjects who were not receiving HRT. The rate of retinal hemorrhages was significantly greater among anastrozole patients compared with tamoxifen and control patients. The prevalence of retinal hemorrhages for anastrozole was estimated at >4% (95% CI). These findings suggest that intraocular imaging techniques may be useful in determining whether aromatase inhibitor therapy may be leading to increased vitreoretinal traction in breast cancer patients receiving this type of treatment.⁷⁹

Addressing Bone Loss with Endocrine Therapy

Gnant and colleagues reported results from an ABCSG-12 substudy that evaluated the use of the bisphosphonate zoledronic acid for prevention of bone loss induced by adjuvant endocrine therapy.⁸⁰ The results reflected follow-up at 2 years after completion of adjuvant therapy in the main ABCSG-12 study. The ABCSG-12 study randomized 1801 patients to one of four treatment arms: tamoxifen and goserelin with or without zoledronic acid and anastrozole and goserelin with or without zoledronic acid. Patients received adjuvant therapy for 3 years. The bone substudy included 404 patients, 201 of whom received adjuvant zoledronic acid together with endocrine therapy and 203 of whom did not. After 3 years of treatment, patients who did not receive zoledronic acid experienced a significant loss of bone mineral density (11.3%) compared with baseline levels (P<.0001). This decrease in bone mineral density was greater in patients who received anastrozole versus tamoxifen (-13.6% versus -9%). Two years after completion of adjuvant therapy, patients who had not received zoledronic acid continued to have significantly decreased bone mineral density compared with baseline levels (-6.8%, P=.0005). For the group of patients who had received zoledronic acid, bone mineral density was unchanged at 36 months and significantly increased (+3.9%, P=.02) at 60 months compared with baseline levels.⁸⁰

Aromatase inhibitor therapy results in almost complete ablation of estrogen production. This can lead to accelerated bone loss and increased risk for fracture. The Z-FAST study examined the effect of zoledronic acid on bone loss associated with aromatase inhibitor therapy. Brufsky and colleagues reported 36-month follow-up data from the study, which was conducted in 602 postmenopausal patients with ER+ and/or PR+ breast cancer who received letrozole.81 Patients were randomized to upfront zoledronic acid (n=189) or zoledronic acid delayed until T score (measure of osteopenia) reached less than -2 or fracture occurred (n=188). The primary endpoint for the study was percent change in lumbar spine bone mineral density at 12 months. Upfront zoledronic acid was associated with a mean increase in lumbar spine bone mineral density of 3.72% compared to a decrease of 2.95% in the delayed group, for a significant absolute difference of 6.7% (P<.001). There was an increase in mean total hip bone mineral density for the upfront group of 1.66% versus a mean decrease of 3.51% for the delayed group, for a significant absolute difference of 5.2% (P<.001). Two percent of patients in the upfront group experienced a decrease in T score compared with 18% in the delayed group. The overall difference in the percentage change in bone mineral density between the upfront and delayed zoledronic acid treatment groups progressively increased from baseline through 36 months. These results suggest that zoledronic acid is effective in the prevention of bone loss associated with aromatase inhibitor therapy.⁸¹

Modeling Relapse Risk With Endocrine Therapy

The overall difference in the percentage change in bone mineral density between the upfront and delayed zoledronic acid treatment groups progressively increased from baseline through 36 months.

A model of relapse risk in patients who received endocrine therapy was developed based on results from a long-term study of neoadjuvant letrozole or tamoxifen in postmenopausal women with estrogen receptor positive (ER+) stage II and III breast cancer too large for breast conservation. Ellis and colleagues reported results from this development effort.⁸² A number of potential factors, including posttreatment ER status, Ki67 proliferation index, histological grade, pathological tumor size, node stage, and treatment response, were evaluated to identify independent predictors for relapse-free survival and overall survival. Since relapse-free survival and overall survival were similar between the neoadjuvant letrozole and tamoxifen treatment arms, the groups were pooled for analysis. The median follow-up for the study was 62.5 months. Multivariate analysis of posttreatment tumor characteristics found six independent predictors of relapse: pathological tumor stage, node status, Ki67 level, tumor grade, ER status, and clinical response. The multivariate predictive model based on these independent predictors was successful in distinguishing between four separate groups with relapse-free survival of 100%, 82%, 52%, and 0%. It provided additional information to discriminate between patients with the extremes of breast cancer outcomes in this setting and demonstrated that 4 months of neoadjuvant endocrine therapy, followed by a response assessment, is a promising approach for predicting the course of ER-positive breast cancer in postmenopausal women.⁸²

Looking to the Future

In the coming years, breast cancer will increasingly be seen and treated as a heterogeneous disease. This will spell the end of large, global neoadjuvant and adjuvant breast cancer treatment studies that approach breast cancer as a homogenous disease entity in favor of smaller studies that focus on treatment of disease subtypes. It is important to realize that to conduct these studies will continue to require screening a large number of patients in order to find the subset that is eligible for a particular study. The era of molecular predictors has already begun. Genomic technologies such as Oncotype DX and other gene signatures help identify subtypes of breast cancers and treatment strategies will increasingly be selected based on these markers. ER-positive highly endocrine sensitive cancers, triple negative disease, and HER2-positive tumors are already considered different disease entities requiring different treatment strategies and clinical trials.

The current first-generation genomic predictors including MammaPrint, Oncotype DX, and several others derive their value from being able to identify a particularly favorable prognostic group among the ER-positive patients and also define another ER-positive group that gains the most benefit from adjuvant chemotherapy. The current proposed chemotherapy response predictors predict chemoresponsiveness in a broad sense and their regimen specificity, if any, is unproven. Unfortunately almost all ER-negative patients are called high risk by MammaPrint or Oncotype DX despite their variable clinical course. Nevertheless, these assays represent a small but important improvement over older clinical variable–based risk prediction methods. When the clinical variable–based and genomic risk predictions are discordant (approximately 30% of all cases), the genomic predictors seem to be more accurate. This is probably due to their ability to better characterize patients with intermediate clinical risk features, in particular those with intermediate histological grade. Equally importantly, they provide an easily interpretable risk score that represents the combined information from multiple variables. This is an important advance over simply listing quantitative ER, PR, HER2, Ki67, and other marker results as it used to be presented in traditional pathology reports.

The available tests already provide us with the opportunity to start to individualize treatment strategies. In the near future, clinical trials may routinely select patients according to molecular phenotype. Different research hypotheses and different therapeutic questions may be appropriate for different genomic groups. This will allow us to apply the currently available and the emerging new therapies more judiciously.

For the next generation of genomic tests, it will be important to try to risk stratify ER- and HER2-negative breast cancers. Combining multiple different genomic predictors including determination of ER and HER-2 status into a single assay could greatly enhance the cost-effectiveness of these tests. There is also a lot of interest to test the hypothesis in the clinic that in vitro cell-line derived, drug-specific response predictors can be developed and can predict response in patients.

In addition, as we understand more about the molecular targets that characterize certain subtypes of breast cancer, we will begin to explore the use biologic treatments in concert with chemotherapy to individualize therapy for these breast cancer subtypes.

At the close of the panel session, Dr. Burstein asked each participant to predict how the recent advances in targeted therapy for breast cancer will influence approaches to treatment in the next 5 years. The faculty provided the following insight:

Dr. Pusztai Dr. Pusztai on molecular prognostic tools: I think that breast cancer will not be treated as a homogeneous disease. It will resemble more the current approach to lymphomas where physicians would not think of doing a general lymphoma study but rather design separate studies for Hodgkin’s lymphoma versus various subtypes of non-Hodgkin’s lymphomas. The current large global adjuvant and neoadjuvant studies may be the last generation of this simplistic approach to breast cancer. Molecular risk and treatment stratification will be more commonly used; several rivals for Oncotype DX will probably appear. Distinct treatment strategies will be adopted for ER-positive endocrine sensitive cancers compared to ER-positive endocrine-insensitive tumors or for triple receptor negative cancers Dr. Budd Dr. Budd on chemotherapy: By 2012, in terms of routine practice, physicians will be routinely doing genomic signatures, perhaps pharmacogenomic signatures, in selecting patients who are candidates for chemotherapy. At some point, I hope physicians will be able to use this to choose the type of chemotherapy. The clinical trials will routinely stratify patients or select patients from some genomic predictor and then try to derive a signature that is predictive of the question at hand. So, there will be a hypothesis presented in a specific genomic group that is tested, but we will be using this to select patients who are candidates for treatment routinely in 5 years. I do not think physicians will be picking particular drugs in 5 years. Although physicians will still be limited in the number of regimens, there will be more judicious application. The question will primarily be integration of biologic treatments with chemotherapy and some of these newer agents that have been discussed, both with chemotherapy and hormonal therapy. Dr. Munster Dr. Munster on endocrine therapy: I hope the future will hold more answers on how long to treat with endocrine therapy and who will benefit. Additionally, it will be important to differentiate the women with ER-positive who will benefit from or need endocrine therapy from those who will not, as has been proposed for chemotherapy. The patients who will benefit from chemotherapy may not benefit from hormonal therapy and vice versa, hence we may need to subdivide the treatment approach further. As we learn to more optimally use hormonal therapy, physicians may in fact better select the population likely to benefit, as physicians did with other targeted therapy. Furthermore, physicians may need to add other targeted therapy to the currently used hormonal manipulations. At present, physicians only use therapy targeting the estrogen receptor. Physicians may need to further address methods to inhibit the progesterone receptor, as well as the down-stream and cross-signaling associated with both of these receptors. Dr. Burstein Dr. Burstein: One of the curious things about the oncotype assay is actually that those high risk patients seem to get negligible benefit from Tamoxifen yet, we still, of course, give them endocrine treatment. Do you think we will have a molecular test that will be so good that it will tell us patients who have an excellent prognosis and do not need endocrine therapy, even though they are ER-positive, or conversely, where they are so resistant to endocrine therapy that you would not recommend it? Dr. Munster: I think we will have a test to tell us who would not benefit from endocrine therapy. I do not think we will have a test to tell us who does not need endocrine therapy. Dr. Arteaga Dr. Arteaga on novel presurgical and neoadjuvant clinical trials: In breast cancer, there are many novel single-agent therapies and combinations in preclinical and clinical development. For the majority, if not all, of these therapies, there is not a clear biomarker profile in tumors that can allow for (1) the selection or exclusion of patients into phase 2 clinical trials with these new drugs or combinations, and (2) the prediction of longer term patient outcome. Data presented at the SABCS 2007 suggest that short presurgical or neoadjuvant, tissue-based pharmacodynamic trials may provide information that can later be used for patient selection and/or identifying the odds of treatment response or failure. For example, administration of antiestrogens for a short period of a few weeks to 4 months and assessment of the proliferative response in situ as measured by Ki67 in the resected cancer, may inform the prediction of the long-term outcome of that individual patient after adjuvant hormonal therapy. It is speculated that this approach, when applied to other agents, may expedite the drug development process and provide tumor material for the open-ended discovery of molecular biomarkers predictive of response or resistance. In this regard, breast cancer may well be at the forefront of tumors where these novel approaches can be tested.

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