Abstract P6-10-07: Family history and risk of pregnancy-associated breast cancer (PABC)

Abstract

Abstract Background: The risk of breast cancer is at least doubled in young women with a family history of breast cancer. Pregnancy has a dual effect on breast cancer risk; a short-term increase followed by a long-term protection. It has been hypothesized that women with a genetic predisposition for breast cancer are particularly susceptible to physiological changes during childbearing that may influence short term risk. Materials & methods: We followed a cohort of women aged 15 to 44 years between 1963 and 2009 identified in Swedish registers. Family history was defined as having a mother or sister with breast cancer. In a case-cohort analysis, we estimated incidence rate ratios of breast cancer during pregnancy and time intervals up to 10 years post-delivery. Results: In 3,452,506 women, there were 15,548 cases of breast cancer (1,208 were pregnancy-associated (PABC), defined as breast cancer during or within 2 years of pregnancy). Compared to nulliparous women, the risk of breast cancer was decreased during pregnancy, similar during 1st year and increased during 2nd year post-delivery. The pattern was similar in women with or without family history of breast cancer. A peak in risk was observed 5-6 years following the first birth regardless of family history. After a second birth, this peak was only present in women with a family history. Conclusions: Our results indicate that women with a family history of breast cancer do not have a different breast cancer risk during and within 10 years following pregnancy compared to women without a family history. Citation Format: Lambe M, Johansson ALV, Andersson TM, Hsieh C-C, Cnattingius S, Dickman PW. Family history and risk of pregnancy-associated breast cancer (PABC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-10-07.