Bilateral mastectomy associated with higher breast cancer mortality among patients with estrogen receptor positive progesterone receptor negative localized breast cancer

Rates of mastectomy for patients with localized breast cancer remain high despite decades of evidence that breast conservation therapy is equally effective. The impact of progesterone receptor (PR) status on the relative efficacy of surgical extent for localized estrogen receptor (ER) positive breast cancer on breast cancer mortality has not been studied. This retrospective cohort study included patients diagnosed with breast cancer between 1998 and 2015 using data from the Surveillance, Epidemiology and End Results (SEER) program. Female patients aged 40-70 with T1-2N0M0 ER positive breast cancer were included. Patients in this study either underwent lumpectomy without radiation, lumpectomy with radiation, unilateral mastectomy without radiation, or bilateral mastectomy without radiation for their disease. Breast cancer specific mortality was the main outcome of interest, calculated using competing risks methods to estimate cumulative incidence and hazard ratios among the treatment groups. After one-to-one matching, 23,080 patients were included with median follow-up time 7.6 years (interquartile range, 4.0-8.3 years). Median age at diagnosis was 52 years (interquartile range, 47-59 years). Among patients, 19,996 (86.6%) had PR+ disease and 3,084 (13.4%) of patients had PR-. Among patients with PR- disease, bilateral mastectomy was associated with higher cumulative incidence of breast cancer mortality relative to patients undergoing lumpectomy with radiation, with 10-year cumulative incidences of 9.2% [95% confidence interval (CI): 6.6-12.7%] vs. 4.4% (95% CI: 3.0-6.6%). This difference was significant in the adjusted multivariate model [hazard ratio (HR) =1.77; 95% CI: 1.12-2.82; P=0.02]. Bilateral mastectomy was associated with significantly increased risk of breast cancer mortality relative to lumpectomy with radiation for patients with PR- disease. Unilateral mastectomy and lumpectomy without radiation were associated with increased risk for breast cancer mortality relative to lumpectomy with radiation for patients with PR+ disease.