Association between contralateral prophylactic mastectomy and breast cancer outcomes by hormone receptor status

Background: The effect of contralateral prophylactic mastectomy (CPM) on the survival of patients with early-stage breast cancer remains controversial. The objective of this study was to evaluate the benefits of CPM using a propensity scoring approach that reduces selection bias from the nonrandom assignment of patients in observational studies. Methods: A total of 3889 female patients with stage I to III breast cancer were identified who were treated at The University of Texas MD Anderson Cancer Center from 1997 to 2009. We assessed the association between CPM and disease-free (DFS) and overall survival (OS), by using Cox proportional hazards models to estimate hazard ratios (HRs), and by matching patients in the CPM and no-CPM groups using propensity scores (n = 497 pairs). Results: With a median follow-up time of 4.5 years, CPM was associated with improved DFS (HR, 0.75; 95% confidence interval [CI], 0.59-0.97) and OS (HR, 0.74; 95% CI, 0.56-0.99), adjusted for prognostic factors. The improved DFS was seen predominantly among hormone receptor-negative (HR, 0.60; 95% CI, 0.38-0.95) compared with hormone receptor-positive patients (HR, 0.80; 95% CI, 0.58-1.10). For the matched patient cohort, stratified survival analysis also showed an improvement in DFS with CPM (HR, 0.48; 95% CI, 0.22-1.01) in hormone receptor-negative patients that was nearly statistically significant. Conclusions: CPM was associated with improved DFS for some patients with hormone receptor-negative breast cancer, after reducing selection bias. Identifying subsets of patients most likely to benefit from CPM may have important implications for a more personalized approach to treatment decisions about CPM.