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Breast-conserving therapy extends OS in early-stage breast cancer
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SAN ANTONIO — Women with early-stage breast cancer who underwent breast-conserving surgery plus radiation therapy achieved significantly better survival outcomes than those who underwent mastectomy without radiation therapy, according to study results presented at San Antonio Breast Cancer Symposium.
Breast-conserving therapy also conferred a significant improvement in distant metastasis-free survival among those with T1N0 disease, defined as tumors up to 2 cm with no nodal involvement.
Sabine Siesling
“Breast-conserving therapy should be the treatment of choice — especially in smaller tumors — when it is medically feasible and according to the patient’s wishes,” Sabine Siesling, PhD, senior researcher at Netherlands Comprehensive Cancer Organisation and professor at University of Twente in the Netherlands, said during a press conference.
Prior randomized controlled trials showed patients with early-stage breast cancer assigned breast-conserving therapy — consisting of surgery with radiation therapy — achieved OS comparable to those assigned mastectomy without radiation therapy. Recent observational studies suggested improved survival with breast-conserving therapy, but these investigations were limited to only 5 years of follow-up.
Siesling and colleagues conducted a population-based study to assess differences in 10-year OS and distant metastasis-free survival between treatments among women with early-stage breast cancer.
The researchers used the Netherlands Cancer Registry to identify patients diagnosed between 2000 and 2004 with primary invasive T1 or T2, N0 or N1, M0 disease treated at one of 90 hospitals in the Netherlands.
The cohort used for the OS analysis included 37,207 women, of whom 21,734 (58.4%) received breast-conserving therapy and 15,473 (41.6%) received mastectomy without radiation. Patients who underwent breast-conserving therapy were younger; were more likely to have smaller, well-differentiated tumors; and were less likely to receive hormonal therapy or axillary lymph node dissection.
Median follow-up was 11.3 years.
Researchers reported improved 10-year OS among patients who underwent breast-conserving therapy (76.8% vs. 59.7%).
The survival benefit associated with breast-conserving therapy persisted after Cox regression analysis adjusted for age, receipt of hormonal therapy and other potential confounding factors (adjusted HR = 0.81; 95% CI, 0.78-0.85). The OS benefit also appeared consistent regardless of T or N stages.
The study also included a subgroup of 7,552 patients diagnosed in 2003 who had active follow-up designed to register all recurrent events within 10 years. In this group, 4,647 (61.5%) underwent breast-conserving therapy and 2,905 (38.5%) underwent mastectomy. Researchers used data from this subgroup to measure 10-year distant metastasis-free survival.
Median follow-up in this cohort was 9.8 years.
Results showed a higher rate of 10-year distant metastasis-free survival among patients who underwent breast-conserving therapy (83.6% vs. 81.5%; adjusted HR = 0.88; 95% CI, 0.77-1.01), but the difference did not reach statistical significance.
An analysis stratified by T and N stage revealed a statistically significant improvement in distant metastasis-free survival with breast-conserving therapy among patients with T1N0 disease (adjusted HR = 0.74; 95% CI, 0.58-0.94).
In the subgroup analysis, patients who underwent mastectomy appeared more likely to experience distant metastases (14.7% vs. 11%; P < .001) and regional recurrences (4% vs. 2.1%; P < .001). Results showed no difference in local recurrence rates between treatment groups.
Siesling acknowledged limitations to the study. Observational studies are prone to confounding by indication, and researchers did not have information about patients’ comorbidities or HER-2 status.
Siesling also emphasized that women who underwent breast-conserving therapy were younger and had more favorable tumor characteristics than those who underwent mastectomy.
“We corrected for all of these factors in the multivariable analyses; however, we cannot completely rule out this phenomenon,” Siesling said in a press release. “In addition, residual confounding caused by nonmeasured factors could also have altered the results. However, we do not expect these factors to overrule the large impact of all variables we included in the analyses.” – by Mark Leiser
Reference:
van Maaren MC, et al. Abstract S3-05. Presented at: San Antonio Breast Cancer Symposium; Dec. 8-12, 2015; San Antonio.
Disclosure: Siesling reports no relevant financial disclosures. Please see the abstract for a full list of all researchers’ relevant financial disclosures.
Perspective
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Charles L. Shapiro, MD
A registry-based study is not a substitute for a properly controlled randomized trial or meta-analysis of all randomized trials comparing breast-conserving surgery with radiation to mastectomy.At least three such meta-analyses have been performed, including one performed by Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) and another one specifically including women aged 40 years and younger. The EBCTCG analysis involved 36 randomized trials with more than 17,000 women. The other analysis included more than 22,000 women aged younger than 40 years who participated in five population-based studies and two randomized trials. There was a measure of consistency in the results of these meta-analyses in that there were no statistically significant differences in the adjusted annual HRs for death between breast-conserving surgery with radiation or mastectomy.
In a post-hoc subset analysis in one of the studies, when more than 50% of women with axillary nodal positivity in both surgical treatment arms received adjuvant radiation, survival rates between them were similar. However, when less than 50% of node-positive patients received adjuvant nodal radiation, results showed a survival advantage for breast-conserving surgery and radiation (OR = 0.69).
The interpretation of post-hoc subset analyses is problematic for several reasons, including selection bias, imbalances in unknown factors, chance alone and the fact treatment allocations are not random.
In the current registry study, we have no information about the use of chest wall radiation after mastectomy or the use of adjuvant chemotherapy, factors known to improve OS. It is possible that those in the node-positive mastectomy group who did not receive radiation and/or adjuvant chemotherapy had poorer survival than the breast-conserving surgery and radiation group. With all of these limitations and caveats, one has to wonder why this abstract merited presentation at an oral session. The more I think about these results, the less confident I am that we actually learned something of value from this large registry study.
References:
Early Breast Cancer Trialists’ Collaborative Group. N Engl J Med. 1995;333:1444-1455.Morris AD, et al. Cancer J Sci Am. 1997;3:6-12.
Vila J, et al. Breast. 2015;doi:10.1016/j.breast.2015.02.002.
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