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

Abstract

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. 111 cases and 74 controls carried BRCA1/2 mutations. Results are reported for non-carriers. Race, body mass index and menopausal status did not differ between cases and controls. Risk of CBC was elevated among women with a first primary with lobular histology (RR=1.5; 95% CI=1.1−2.2). Grade 2 (RR 0.6, 95% CI 0.5−0.9) and grade 3 tumors (RR 0.6, 95% CI 0.4−0.9) were associated with a lower risk of CBC compared to grade 1 tumors. ER status was not significantly associated with CBC, but only 35% of ER positive patients received tamoxifen. These results were not modified by age at diagnosis (<45, ≥45) or family history of breast cancer. The proportion of in situ CBC increased from 18.2% between 1985−1988 to 22.0% between 1997−2000 (p=0.04). Conclusions: In this large population based study, women with an initial diagnosis of lobular cancer or low grade histology were at increased risk of CBC in the absence of widespread use of endocrine therapy. Given the known benefit of endocrine therapy in reducing CBC, our findings suggest that consideration of standard tumor characteristics alone in women without BRCA1/2 mutations do not identify a subset of women likely to benefit from CPM.