Effect of hormone receptor status and local treatment on overall survival for early-stage breast cancer.

Abstract

60 Background: Mastectomy and breast conserving therapy (BCT) have been established as interventions with equivalent survival for early stage breast cancer. However, trials comparing these approaches pre-date the understanding of breast cancer heterogeneity. We hypothesized that if heterogeneity is considered, the surgical approach may impact survival. Methods: Using the National Cancer Database (NCDB) from 2004 to 2005, we evaluated the overall survival (OS) of women with Stage I breast cancer who underwent mastectomy, BCT (surgery with radiation), or breast conserving surgery (BCS, surgery without radiation). Since only ER and PR data were available, we categorized tumors as ER and/or PR positive (HR+) or ER and PR negative (HR-). We performed propensity score-matched analysis using the covariates associated with the choice of surgical therapy. We used the Cox proportional hazards model for analyses of OS in pre-matched and matched cohorts. Double robust estimation under the Cox model was used in the analyses of the matched cohort. Results: A total of 16,646 female patients met study criteria: 1,845 (11%) received BCS, 11,214 (67%) received BCT, and 3,587 (22%) underwent mastectomy. Patients undergoing BCT had superior survival outcomes compared to those undergoing mastectomy or BCS (5-year OS was 96% vs 90% vs 87% respectively, p<0.001). After adjusting for other risk factors, BCT remained significantly associated with OS (HR 0.57 [95% CI 0.50, 0.66] for BCT vs BCS; HR 0.67 [95% CI 0.6, 0.76] for BCT vs mastectomy). In the matched cohort (1706 patients in each treatment group), comparison of OS in multivariate analysis confirmed the survival benefit associated with BCT over mastectomy (HR 0.73 [95% CI, 0.59, 0.89]) in the HR+ subset but not in the HR- subset (HR 0.91 [95%CI 0.62, 1.34]) of patients. BCT showed better OS than BCS in both HR+ and HR- subsets (HR 0.63 [95% CI, 0.52, 0.77], HR 0.67 [95%CI 0.46, 0.98] respectively). No differences were seen in OS between mastectomy and BCS in either HR+ or HR- cohorts (HR 0.87 [95%CI. 0.73, 1.03]), HR 0.73 [95%CI 0.51, 1.06] respectively). Conclusions: When tumor heterogeneity is considered, type of local therapy appears to impact the survival of women with Stage I breast cancer.