KRAS developments and implementation of findings

The Holy Grail of oncology is the ability to predict which treatments will be effective for a given patient and spare the toxicity, time and expense of futile therapies. In colorectal cancer, tumor Kirsten ras (KRAS) gene mutational status has recently emerged as a biomarker of nonresponse to therapies targeting the epidermal growth factor receptor. With a convincing collection of retrospective but robust data culminating in the plenary session presentation of KRAS subgroup analysis from the phase-3 CRYSTAL trial at this year’s ASCO Annual Meeting, tumor KRAS testing has crept into the clinical arena. Entering into this uncharted territory towards personalized medicine for colorectal cancer, clinicians must now address the unanswered questions of how, which and when.

OPUS and CRYSTAL

The advent of EGFR-directed monoclonal antibody therapy in metastatic colorectal cancer renewed interest in KRAS, based upon the rational premise that alterations downstream in a signaling pathway may influence response to an upstream targeted therapy. Approximately 30% to 50% of colorectal cancer specimens harbor a mutation in the KRAS gene on chromosome 12. In a seminal retrospective analysis of banked tumor specimens from 30 patients receiving the EGFR-targeting monoclonal antibody cetuximab (Erbitux, ImClone) alone or in combination with other therapies, Lievre and colleagues identified an association between KRAS mutation and lack of response to cetuximab-based chemotherapy, with almost 70% of nonresponders and none of the responders harboring a mutation (P=.0003). Subsequently, multiple other predominantly retrospective series have shown similarly robust associations between KRAS mutational status and lack of response to cetuximab and another EGFR antibody panitumumab (Vectibix, Amgen).

Alan P. Venook

The strength of this association has now been corroborated in retrospective analyses of patients treated in the randomized, prospective, phase-3 setting. Amado and colleagues found that patients with metastatic colorectal cancer whose tumors had KRAS mutations demonstrated no response to panitumumab monotherapy. By comparison, those patients with KRAS wild-type (normal gene) tumors demonstrated a 17% response rate. The hazard ratio for the primary endpoint, progression-free survival, was 0.45 with panitumumab in the KRAS wild-type group, by comparison with 0.99 in the KRAS mutant patients. Similarly, a phase-3, randomized trial of cetuximab monotherapy vs. best supportive care in patients with metastatic colorectal cancer conducted by the National Cancer Institute of Canada Clinical Trials Group (NCIC-CTG) and the Australasian Gastrointestinal Trials Group (AGITG) showed no benefit from cetuximab in KRAS mutant patients. In contrast, patients with KRAS wild-type benefitted with cetuximab therapy in comparison with best supportive care, with prolonged PFS of 3.8 vs. 1.9 months (P<.0001), and prolonged overall survival of 9.5 vs. 4.8 months, respectively (P<.0001).

At the 2008 ASCO meeting, data from unplanned subgroup analyses of the phase-3 CRYSTAL trial and the randomized, phase-2 OPUS trial demonstrated an association between KRAS mutational status and response with addition of cetuximab to first-line FOLFIRI and FOLFOX, respectively, in patients with metastatic colorectal cancer. In the CRYSTAL trial, 540 patients were evaluated for KRAS mutation; 35.6% harbored mutations. Among the KRAS wild-type patients, addition of cetuximab improved PFS over FOLFIRI alone, with median PFS of 9.9 vs. 8.7 months (HR=0.68; P=.017). There was no benefit with addition of cetuximab in KRAS mutant patients, with a nonsignificant trend toward shorter PFS in the cetuximab-treated troup (HR=1.07, P=.47).

In the OPUS trial which evaluated effect of cetuximab in combination with FOLFOX, 42% of patients harbored KRAS mutation. In the KRAS wild-type patients, addition of cetuximab produced significant improvements in response rate and PFS, while no benefit was derived by the KRAS mutant patients.

CAIRO2

A notable exception in the KRAS story was the CAIRO2 study, a randomized, phase-3 trial that evaluated the combination of capecitabine (Xeloda, Roche), oxaliplatin (Eloxatin, Sanofi Aventis), and bevacizumab (Avastin, Genentech) with or without cetuximab in the first-line setting for metastatic colorectal cancer. Unlike the CRYSTAL and OPUS trials, there was no benefit in PFS with the addition of cetuximab to patients with KRAS wild-type tumors. Again, the KRAS mutant patients appeared to have worse outcomes with the addition of cetuximab.

It is unclear why the results from CAIRO2 diverge from the multitude of other trials. Possibilities include a negative interaction between the biologic agents bevacizumab and cetuximab, an imbalance in randomization despite similar baseline characteristics between groups, or differences in duration of therapy. The ongoing phase-3, randomized Cancer and Leukemia Group B (CALGB) trial 80405 may help to answer this question by comparing first-line 5-FU–based combination therapy with or without cetuximab, bevacizumab, or the combination of both biologic agents in metastatic colorectal cancer. This trial has been amended to include only patients whose tumors are confirmed KRAS wild-type. Similar modifications to include KRAS biomarker testing are underway in trials of cetuximab in colorectal cancer in both the adjuvant and metastatic settings.

Several interesting points arise from these studies. KRAS mutant patients treated with cetuximab fared worse than those treated with standard chemotherapy in CRYSTAL, OPUS and CAIRO2, though the trends were not statistically significant. It is also noteworthy that in CRYSTAL, OPUS, and CAIRO2, as well as in the phase-3 studies of both cetuximab and panitumumab as monotherapy, patients in the control arms had similar outcomes regardless of KRAS status suggesting that KRAS is not an independent prognostic factor.

Applying the data to practice

Based upon thess data, patients with advanced colorectal cancer should undergo tumor KRAS testing prior to receiving EGFR-targeted therapies. KRAS mutational status in metastatic tumor tissue demonstrates high concordance with that of primary tumors, suggesting that any available tissue is adequate for testing. Patients with a known KRAS mutation should not be treated with cetuximab or panitumumab.

These new recommendations have generated a surge in KRAS mutational analysis requests. There are a number of commercial laboratories offering tumor KRAS mutational analysis in the United States and a testing kit is available. Analysis is performed on formalin-fixed, paraffin-embedded tumor tissue; it is also possible to test precut slides or snap-frozen, fresh tissue. Future research may identify other activating mutations to include in KRAS tumor testing.

Several pragmatic concerns arise with the implementation of routine KRAS testing prior to treatment with EGFR-directed therapy. Should patients be treated with EGFR-based therapies during the delay before KRAS mutational analysis results are available? If inadequate tumor tissue is available for testing, should repeat biopsy be attempted in order to ascertain KRAS mutational status? Should all patients with metastatic colorectal cancer be tested at the time of diagnosis to ensure KRAS status is known, even before plans to treat with EGFR inhibition?

Given the possibility of poorer outcomes with EGFR-targeted therapies in patients with KRAS mutation in the subgroup analyses presented above as well as the potential for needless toxicity, we do not recommend initiating therapy with cetuximab or panitumumab until KRAS results are known. In this vein, strong consideration of repeat biopsy attempt should be considered prior to initiating therapy with cetuximab or panitumumab in patients with metastatic colorectal cancer who do not have sufficient archived tissue specimens available for testing. Patients with inaccessible or high-risk sites for repeat biopsy present a dilemma and should be addressed on a case-by-case basis at present. In the future, the increased volume of and experience with KRAS testing should result in greater availability and expedience, potentially enabling the routine testing of tumor tissue at the time of diagnosis for all patients with metastatic disease who may someday be candidates for EGFR-targeted therapy.

In conclusion, the evolution of KRAS is an exciting step towards personalized medicine in advanced colorectal cancer. The overwhelming weight of data reviewed above has answered the questions of which patients to test and when. Prior to embarking upon EGFR-targeted therapy, all patients with metastatic colorectal cancer should undergo tumor testing for this biomarker in order to spare the toxicity, time, and expense in the 30% to 50% of patients whose tumors will harbor a mutation. Oncologists and pathologists must now collaborate to escort KRAS testing from the clinical trial setting into the community.

Alan P. Venook, MD, is Professor of Clinical Medicine and Associate Chief, Division of Medical Oncology, University of California, San Francisco and is also a member of the HemOnc Today Editorial Board.

Robin Kate Kelley, MD, is a Fellow in the Department of Hematology/Oncology at the University of California, San Francisco.

For more information:

• van Cutsem E LI, D’Haens G, Moiseyenko V, et al. KRAS status and efficacy in the first-line treatment of patients with metastatic colorectal cancer treated with FOLFIRI with or without cetuximab: The CRYSTAL experience. Presented at: 2008 ASCO Annual Meeting; Chicago; May 30-June 3, 2008.
• Amado RG, Wolf M, Peeters M, et al. Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer. J Clin Oncol. 2008;26:1626-1634.
• Andreyev HJ, Norman AR, Cunningham D, et al. Kirsten ras mutations in patients with colorectal cancer: the multicenter “RASCAL” study. J Natl Cancer Inst. 1998;90:675-684.
• Frattini M, Balestra D, Suardi S, et al. Different genetic features associated with colon and rectal carcinogenesis. Clin Cancer Res. 2004;10:4015-4021.
• McDermott U, Longley DB, Johnston PG. Molecular and biochemical markers in colorectal cancer. Ann Oncol. 2002;13Suppl4:235-245.
• Lievre A, Bachet JB, Le Corre D, et al. KRAS mutation status is predictive of response to cetuximab therapy in colorectal cancer. Cancer Res. 2006;66:3992-3995.
• Benvenuti S, Sartore-Bianchi A, Di Nicolantonio F, et al. Oncogenic activation of the RAS/RAF signaling pathway impairs the response of metastatic colorectal cancers to anti-epidermal growth factor receptor antibody therapies. Cancer Res. 2007;67:2643-2648.
• De Roock W, Piessevaux H, De Schutter J, et al. KRAS wild-type state predicts survival and is associated to early radiological response in metastatic colorectal cancer treated with cetuximab. Ann Oncol. 2008;19:508-515.
• Di Fiore F, Blanchard F, Charbonnier F, et al. Clinical relevance of KRAS mutation detection in metastatic colorectal cancer treated by Cetuximab plus chemotherapy. Br J Cancer. 2007;96:1166-1169.
• Frattini M, Saletti P, Romagnani E, et al. PTEN loss of expression predicts cetuximab efficacy in metastatic colorectal cancer patients. Br J Cancer. 2007;97:1139-1145.
• Khambata-Ford S, Garrett CR, Meropol NJ, et al. Expression of epiregulin and amphiregulin and K-ras mutation status predict disease control in metastatic colorectal cancer patients treated with cetuximab. J Clin Oncol. 2007;25:3230-3237.
• Lievre A, Bachet JB, Boige V, et al. KRAS mutations as an independent prognostic factor in patients with advanced colorectal cancer treated with cetuximab. J Clin Oncol. 2008;26:374-379.
• Personeni N DSJ, De Hertogh G, Debiec-Rychter M, et al. Response prediction to cetuximab-based therapy: The role of EGFR copy number by fluorescence in situ hybridization and downstream effectors gene mutations. Presented at: ASCO Gastrointestinal Cancers Symposium; 2007.
• Stoehlmacher J MU, Jakob C, Stix B, et al. KRAS mutations, EGFR polymorphisms, and polymorphisms of immunoglobulin fragment C receptor as predictors for response to cetuximab containing chemotherapy in colorectal cancer patients. Identification of new KRAS mutation in codon 12. Presented at: ASCO Gastrointestinal Cancers Symposium; 2008.
• Tabernero J CA, Ciardiello F, Vega-Villegas E, et al. Correlation of efficacy to KRAS status (wt vs. mut) in patients (pts) with metastatic colorectal cancer (mCRC) treated with weekly (q1w) and q2w schedules of cetuximab combined with FOLFIRI. Presented at: ASCO Gastrointestinal Cancers Symposium; 2008.
• Viret F SB, Esteyries A, Lagarde G, et al. Genetic predictors of cetuximab response in metastatic colorectal cancer. Presented at: ASCO Gastrointestinal Cancers Symposium; 2008.
• Jonker D, et al. The influence of K-RAS exon 2 mutations on outcomes in a randomized phase III trial of cetuximab + best supportive care (BSC) versus BSC alone in patients with pre-treated metastatic EGFR-positive colorectal cancer (NCIC CTG CO.17). Presented at: World Congress on Gastrointestinal Cancer; Barcelona, Spain; 2008.
• Bokemeyer C BI, Hartmann J, De Braud F, et al. KRAS status and efficacy of first-line treatment of patients with metastatic colorectal cancer (mCRC) with FOLFOX with or without cetuximab: The OPUS experience. Presented at: 2008 ASCO Annual Meeting; Chicago; May 30-June 3, 2008.
• Punt C TJ, Rodenburg C, Cats A, et al. Randomized phase III study of capecitabine, oxaliplatin, and bevacizumab with or without cetuximab in advanced colorectal cancer (ACC), the CAIRO2 study of the Dutch Colorectal Cancer Group (DCCG). Presented at: 2008 ASCO Annual Meeting; Chicago; May 30-June 3, 2008.
• Etienne-Grimaldi MC, Formento JL, Francoual M, et al. K-Ras mutations and treatment outcome in colorectal cancer patients receiving exclusive fluoropyrimidine therapy. Clin Cancer Res. 2008;14:4830-4835.