Population-based study of contralateral prophylactic mastectomy and survival outcomes of breast cancer patients.

BACKGROUND: Despite increased demand for contralateral prophylactic mastectomy (CPM), the survival benefit of this procedure remains uncertain.

METHODS: We used the Surveillance, Epidemiology, and End Results database to identify 107 106 women with breast cancer who had undergone mastectomy for treatment between 1998 and 2003 and a subset of 8902 women who also underwent CPM during the same period. Associations between predictor variables and the likelihood of undergoing CPM were evaluated by use of chi(2) analyses. Risk-stratified (estrogen receptor [ER] status, stage, and age) adjusted survival analyses were performed by using Cox regression. Statistical tests were two-sided.

RESULTS: In a univariate analysis, CPM was associated with improved disease-specific survival (hazard ratio [HR] of death = 0.63, 95% confidence interval [CI] = 0.57 to 0.69; P < .001). Risk-stratified analysis showed that this association was because of a reduction in breast cancer-specific mortality in women aged 18-49 years with stages I-II ER-negative cancer (HR of death = 0.68, 95% CI = 0.53 to 0.88; P = .004). Five year-adjusted breast cancer survival for this group was improved with CPM vs without (88.5% vs 83.7%, difference = 4.8%). Although rates of contralateral breast cancer among young women with stages I-II disease undergoing CPM were independent of ER status, women with ER-positive tumors in the absence of prophylactic mastectomy also had a lower overall risk for contralateral breast cancer than women with ER-negative tumors (0.46% vs 0.90%, difference = 0.44%; P < .001).

CONCLUSIONS: CPM is associated with a small improvement in 5-year breast cancer-specific survival mainly in young women with early-stage ER-negative breast cancer. This effect is related to a higher baseline risk of contralateral breast cancer.