Abstract 622: Reproductive factors and breast cancer risk to women in Ghana, West Africa

Background: Women of African ancestry have a higher proportion of early onset and estrogen receptor (ER) negative cancers compared to women of European descent. Differences in risk associations by age at onset and ER status for reproductive factors, particularly parity and breastfeeding, have been proposed as possible contributors to this racial disparity. We therefore investigated these relations in the Ghana Breast Health Study. Methods: The study population included 1,126 women diagnosed with invasive breast cancer and 2,106 population controls aged 18-74 years at recruitment (2013-2015) in three hospitals in Accra and Kumasi, Ghana. Factors evaluated included age at menarche, number of livebirths, age at first livebirth, and median months breastfeeding per pregnancy. Odds ratios (OR) and 95% confidence intervals (CI) were estimated using logistic regression models overall and stratified by age. Associations by ER status were estimated using polytomous logistic regression models. Results: We observed associations with parity and extended breastfeeding duration per pregnancy that were modified by age at onset ( 50 years, P-het 5 v. 0 livebirths, but there was no association with breastfeeding months per pregnancy (>18 vs 50 years, both higher number of livebirths and longer durations of breastfeeding months per pregnancy were associated with lower breast cancer risk: OR (95%CI) = 0.40 (0.20-0.83) for >5 vs 0 livebirths and 0.71 (0.51-0.98) for >18 vs 18 vs Conclusion: In this population of women in West Africa, increased number of live births and breastfeeding months per pregnancy were strong protective factors for later onset breast cancer. Among younger women, these trends were modified by ER status, with opposite associations for parity in ER+ vs. ER- tumors and an inverse association with breastfeeding in the ER- tumors that was not seen in the ER+ tumors. Our data support previous reports in African-American women of differential associations of parity and breastfeeding by ER status and age at onset. Further attention should focus on how reproductive factors contribute to observed racial heterogeneity in breast cancer. Citation Format: Jonine D. Figueroa, Brittny Davis Lynn, Lawrence Edusei, Nicolas Titiloye, Ernest Adjei, Joe Nat Clegg-Lamptey, Beatrice Wiafe-Addai, Baffour Awuah, Montserrat Garcia-Closas, Louise A. Brinton. Reproductive factors and breast cancer risk to women in Ghana, West Africa [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 622.