Association between lifestyle, menstrual/reproductive history, and histological factors and risk of breast cancer in women biopsied for benign breast disease.

PURPOSE: Women with benign breast disease (BBD) have an increased risk of subsequent breast cancer. However, whether conventional breast cancer risk factors influence risk of breast cancer among women with BBD is unclear. In this study, we investigated the associations of lifestyle, menstrual/reproductive, and histological factors with risk of breast cancer among women biopsied for BBD.

METHODS: We conducted a case-control study, nested within a cohort of 15,395 women biopsied for BBD at Kaiser Permanente Northwest between 1971 and 2006. Cases were women who developed a subsequent invasive breast cancer during follow-up; controls were individually matched to cases on age at BBD diagnosis. A total of 526 case-control pairs were included in the study. We calculated crude and multivariable OR and 95% CI for the associations between lifestyle, menstrual/reproductive, and histological factors and breast cancer risk using conditional logistic regression.

RESULTS: Compared to premenopausal women, postmenopausal women had reduced risk of subsequent breast cancer (OR 0.60; 95% CI 0.39-0.94), whereas women who ever used hormone replacement therapy (HRT) had increased risk (OR 3.61; 95% CI 1.68-7.75), as did women whose BBD lesion showed atypical hyperplasia (OR 5.56; 95% CI 2.05-15.06). Smoking, BMI, early menarche, multiparity (≥4), history of oophorectomy, and extent of lobular involution were not associated with risk of breast cancer.

CONCLUSION: This study suggests that use of HRT and having atypical hyperplasia are associated with increased risk of breast cancer among women with BBD, while postmenopausal women with BBD have a reduced risk.