Patient and tumor characteristics associated with contralateral breast cancer in a nested population-based case-control study.

1014 Background: The identification of patient and tumor characteristics associated with an increased risk of contralateral breast cancer (CBC) would be useful for counseling women with unilateral breast cancer (UBC) regarding risks and benefits of contralateral prophylactic mastectomy (CPM), a procedure increasingly chosen by young women. Methods: The WECARE (Women’s Environmental Cancer and Radiation Epidemiology) study is a multicenter, population-based study of 708 cases with metachronous CBC and 1,399 matched controls with UBC nested within a cohort of 52,536 women under age 55 at diagnosis of an initial breast cancer between 1985−2000. Family history was collected by phone interviews; treatment and tumor characteristics were abstracted from medical records, and germline DNA was tested for deleterious mutations of BRCA1/2. Multivariable adjusted rate ratios (RR) and 95% confidence intervals (CI) were estimated using conditional logistic regression. Results: The median age of cases and controls was 46...