Use of Bisphosphonates and Risk of Postmenopausal Breast Cancer.

Abstract Background Bisphosphonates are commonly used for the treatment of osteoporosis and for prevention and treatment of skeletal lesions due to malignancy. However the association between the use of bisphosphonates and the risk of developing breast cancer has not been reported.Methods The Breast Cancer in Northern Israel Study (BCINIS) is a population-based case-control study in northern Israel of breast cancer cases and age/clinic/ethnic-group matched controls. Use of bisphosphonates for at least 5 years was assessed in 4,575 postmenopausal cases and controls using a structured interview. It was further validated by data from prescription records among participants for whom they were available.Results The self-reported long-term use of bisphosphonates prior to diagnosis was associated with a significantly reduced relative risk of breast cancer (Odds Ratio=0.66, 95% CI: 0.47-0.93). This association remained significant in a pharmacy records based analysis after adjustment for age, fruit and vegetable consumption, sports activity, family history of breast cancer, ethnic group, BMI, use of calcium supplements, HRT use, number of pregnancies, months of breast feeding and age at first pregnancy (OR=0.71, 0.57-0.90). A significant dose response association between length of use of bisphosphonates and breast cancer risk was found. Breast tumors identified in bisphosphonates users were more often ER positive and less often poorly differentiated.Conclusions The use of bisphosphonates for more than 1 year was associated with a 29% relative reduction in the risk of postmenopausal breast cancer. Tumors developing under bisphosphonates treatment tended to have a favorable prognostic factors profile. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 27.