Incidence and outcomes of contralateral breast cancers

Background: The significance of a contralateral breast cancer is largely unknown, making prophylactic mastectomy controversial. Methods: Differences between stages of initial and contralateral cancers were determined by t test. Survival distributions were compared by log-rank analyses and compared with Surveillance Epidemiology and End Results data for unilateral cancers. Results: Metachronous contralateral cancers occurred at a rate of .13% per year and were of significantly lower stage. Metachronous cancers adversely impacted survival for patients with low-stage initial cancers, but the interval between cancers was less than 36 months. Synchronous tumors occurred in 2.3% of patients; survival was worse than for patients with metachronous cancers. Conclusions: Prophylactic mastectomy is unlikely to be beneficial because of the lower stages and low incidence of second cancers, even for patients with initial low-stage cancers.