Contralateral breast cancer: Effect of stage on survival after unilateral breast cancer.

69 Background: Contralateral breast cancer (CBC) is the most common malignancy among breast cancer survivors. We investigated the impact of CBC on overall survival (OS) after unilateral primary breast cancer (UPBC) in women treated with mastectomy. Methods: Using the Surveillance Epidemiology End Results registry, we identified women age 25-80 diagnosed 1998-2006 with UPBC stage 0-III, treated with mastectomy and free of CBC at 1-year landmark. Subjects were split into test and validation samples. Follow-up continued until the earliest occurrence: death, end of 2008, or age 85. Primary risk factor was incident CBC, a time-dependent variable categorized as advanced-stage (IIB-IV), early-stage (0-IIA), or none. Proportional hazards regression adjusted for primary tumor characteristics, treatment including contralateral prophylactic mastectomy (CPM), demographics, and aging. Results: Subjects (n= 109,411, age 53.7[+12.7] years at UPBC diagnosis) were followed median 51 months. Most UPBC were early stage (63%...