Abstract 2747: Increasing age at first full-time pregnancy correlates to use of oral contraceptives before age 20 in women with a family history of breast cancer

Abstract

Abstract Background Women with a family history of breast cancer (BC) in first-degree female relatives have an increased risk of BC. The aim of this study was to determine the BC risk associated with exposure to endogenous and exogenous hormones in familial BC compared with non-familial BC. Materials and methods A population-based prospective questionnaire-based cohort was initiated in 1990 in the South Swedish Health Care Region. Forty thousand healthy women between ages 25 to 65 years were randomly selected, out of which 29,520 answered the first questionnaire. Data was subsequently collected from several registries and a second questionnaire. Familial BC was defined as having first-degree relatives (mother, sisters, and/or daughters) diagnosed with BC. Known mutation carriers in BRCA-related genes (n = 13) were excluded from all analyses. To determine whether there are any differences between familial and non-familial BC risk according to hormonal exposures, Cox proportional hazard models were used. Hazard ratios (HR) were estimated with 95% confidence intervals (CI), and all models were adjusted for birthdate. Results At the end of follow-up (10/31/2013), 1,500 (5%) of the women were diagnosed with BC. Out of the 1,500 BC cases, 192 women (13%) had a family history of BC. Having a family history of BC in first-degree relatives was twice as prevalent among BC cases compared with women without BC diagnosis (OR 1.9 (CI 1.63-2.23)). When adjusting for age at menarche and ever-use of oral contraceptives (OC), an increased age at first full-time pregnancy was associated with an increased risk of BC, both for BC cases with familial BC and non-familial BC, HR 1.02 (CI 1.00-1.03) and HR 1.01 (CI 1.00-1.02), respectively. Adjusted for age at menarche and parity, an increased risk of BC was associated with use of OC before age 20 (HR 1.7 (CI 0.99-2.80)) for BC cases with familial BC compared with non-BC cases with familial BC. This was not observed in women with non-familial BC. Conclusion The main findings in this study were that older age at first full-time pregnancy has a larger impact on BC risk in women with familial BC than in women without, and that use of OC before age 20 increases the risk of BC in women with familial BC, not observed in women without. Well known familial and/or hormonal risk factors for BC were observed in our study, implying the validity of the cohort. Our results indicate similarities in risk of BC between women with, and without, familial BC regarding age at first full-term pregnancy. However, the impact seems to be larger in familial BC. If confirmed in other studies, our findings could be of interest for women with familial BC, especially regarding the increased risk when using OC during adolescence, where other alternatives are available. Citation Format: Annelie Augustinsson, Carolina Ellberg, Ulf Kristoffersson, Håkan Olsson. Increasing age at first full-time pregnancy correlates to use of oral contraceptives before age 20 in women with a family history of breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2747. doi:10.1158/1538-7445.AM2015-2747