Association between unilateral or bilateral mastectomy and breast cancer death in patients with unilateral ductal carcinoma

BACKGROUND: Utilization of bilateral mastectomy for unilateral breast cancer is increasing despite cost and surgical risks with conflicting reports of survival benefit. Current studies evaluating death after bilateral mastectomy have included patients treated both with breast conservation therapy and unilateral mastectomy. In this study, we directly compared breast cancer–specific death of patients who underwent bilateral or unilateral mastectomy for unilateral breast cancer using a matched cohort analysis. METHODS: This was an observational study of women diagnosed with unilateral breast cancer from 1998 through 2002, using the Surveillance, Epidemiology, and End Results (SEER) database. A 4-to-1 matched cohort of patients was selected including 14,075 patients. Mortality of the groups was compared using Cox proportional hazards models for cause-specific death. RESULTS: A total of 41,510 patients diagnosed with unilateral breast cancer were included. Unilateral mastectomy was performed in 93% of patients, while bilateral mastectomy was performed in the remaining 7% of patients. When 4-to-1 matching was performed, 11,260 unilateral mastectomy and 2,815 bilateral mastectomy patients were included. Patients with bilateral mastectomy did not have a significantly lower hazard of breast cancer–specific death when compared with patients with unilateral mastectomy (hazard ratio: 0.92 vs 1.00, p=0.11). CONCLUSION: Bilateral mastectomy did not provide a clinically or statistically significant breast cancer–specific mortality benefit over unilateral mastectomy based on a matched cohort analysis of a nationwide population database. These findings should be interpreted in the context of patient preference and alternative benefits of bilateral mastectomy.