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

Abstract

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%), moderately/poorly differentiated (78%), ER+PR+ (52%). Few (9.8%) women underwent CPM at primary diagnosis. Incident CBC (n=867, 0.79%) was diagnosed median 23.5 (95% CI 1.2-72) months beyond the 1-year landmark. Test and validation samples did not differ. Only CBC of stage IIB-IV increased mortality; early stage CBC had no effect on OS. Among CBC cases, advanced stage was independently associated with aggressive UPBC (more positive nodes; larger tumor; greater extension), African-American race, and shorter time from UPBC. Conclusions: Among women who undergo mastectomy +/-CPM for UPBC, few develop CBC, which impacts survival only when diagnosed at advanced stage. Efforts to improve survival after UPBC should emphasize earlier detection and prevention of advanced-stage CBC, especially in African-American women and women with more aggressive UPBC. [Table: see text]