Abstract 1779: Risk factors for early-onset ER- and ER+ breast cancer in African American women

Abstract Introduction: Relative to white women, African American (AA) women have a disproportionately high incidence of early-onset breast cancer, particularly higher incidence of aggressive breast cancer subtypes such as estrogen receptor (ER) negative tumors. Elucidation of risk factors for early-onset of specific subtypes of breast cancer is needed. Methods: We evaluated associations of reproductive and lifestyle factors with early-onset invasive breast cancer, defined as diagnosis before age 50, in 47,212 AA women ages 21-49 in the Black Women's Health Study (BWHS). The BWHS is an ongoing prospective cohort study in the U.S. that began in 1995. Risk factor information is updated every two years via mailed questionnaires. Incident cases were self-reported on biennial questionnaires or identified through death records and confirmed by medical records and cancer registry data. Through 2013, we identified 192 ER- and 322 ER+ invasive breast cancers diagnosed before age 50. We used multivariable Cox proportional hazards regression, stratified by age, to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations of family history of breast cancer, age at menarche, parity, age at first birth, years since last birth, lactation, body mass index (recent and at age 18), waist-to-hip ratio, oral contraceptive use, alcohol consumption, smoking history, and physical activity, with risk of ER- and ER+ early-onset breast cancer, separately. Results: The strongest associations were observed for family history of breast cancer, early age at menarche, and lower body mass index at age 18, and these factors were associated with increased incidence of both ER- and ER+ breast cancer. Oral contraceptive use within the past 10 years was also associated with increased risk of both subtypes. High waist-to-hip ratio (HR for top tertile vs. bottom: 1.46, 95% CI: 0.98, 2.19) and high parity (HR for 3+ births vs. 1: 1.43, 95% CI: 0.88, 2.32) were associated with increased risk of ER- breast cancer, while breastfeeding was associated with a reduced risk (HR for ever vs. never: 0.68, 95% CI: 0.47, 0.97). In contrast, higher parity was associated with a reduced risk of ER+ cancer (HR for 3+ births vs. 1: 0.68, 95% CI: 0.45, 1.01). Recent pregnancy (HR for <10 years vs. 10 or more years: 1.33, 95% CI: 0.94, 1.88) and greater alcohol consumption (HR for 7+ drinks/week vs. <1/week: 1.33, 95% CI: 0.81, 2.17) were associated with an increased risk of ER+ tumors. Conclusions: Differential associations of risk factors for ER- vs. ER+ breast cancers in young AA women suggest etiological heterogeneity by tumor subtypes. These differences could explain, in part, disparities in breast cancer incidence and mortality between black and white women. Some identified risk factors are potentially modifiable, suggesting possible opportunities for prevention. Citation Format: Kimberly A. Bertrand, Lynn Rosenberg, Julie R. Palmer. Risk factors for early-onset ER- and ER+ breast cancer in African American women. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1779.