Body Mass Index and Breast Cancer Risk Among Pre- and Postmenopausal BRCA1/2 Mutation Carriers

Thesis (Master's)--University of Washington, 2019Background: BRCA1/2 mutation carriers are at increased risk for breast cancer. It is of interest whether this risk is further impacted by body size, a well-established mediator in breast cancer pathology among the general population. While obesity is a positive predictor of postmenopausal breast cancer, it tends to be inversely associated with premenopausal breast cancer. The purpose of this study was to characterize BMI and compare the risk of incident pre- and postmenopausal breast cancer among normal weight and overweight/obese BRCA1/2 mutation carriers. Methods: BMI was characterized among 359 BRCA1/2 mutation carriers using medical and lifestyle survey data. Longitudinal data on breast cancer incidence was collected via retrospective medical record review for 49 of these carriers, followed for a mean duration of 5.3 years. Incident breast cancer risk relative to BMI was calculated and compared among pre- and postmenopausal carriers. Results: Subjects had a mean BMI of 26.3 kg/m2, and nearly half (46.7%) were classified as overweight or obese. Among subjects followed for incident breast cancer diagnoses, no differences were observed in total incident breast cancer risk among subjects classified as normal weight and overweight/obese. After stratification by menopausal status, no differences were found in the risk of incident postmenopausal breast cancer relative to BMI, while there was a non-significant protective effect of overweight/obesity for premenopausal breast cancer. Conclusion: BMI was not associated with breast cancer risk among pre- or postmenopausal BRCA1/2 mutation carriers. However, nearly half of BRCA1/2 mutation carriers may be impacted by overweight or obesity, suggesting the importance of further research to inform preventative recommendations for this high-risk population