Purpose: 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.
Patients and methods: The Breast Cancer in Northern Israel Study is a population-based case-control study in northern Israel of patients with breast cancer and age-, clinic-, and ethnic-group matched controls. Use of bisphosphonates was assessed in 4,039 postmenopausal patients and controls, members of Clalit Health Services, using pharmacy records.
Results: The use of bisphosphonates for longer than 1 year before diagnosis, but not for shorter than 1 year, was associated with a significantly reduced relative risk of breast cancer (odds ratio [OR], 0.61; 95% CI, 0.50 to 0.76). This association remained significant after adjustment for age, fruit, and vegetable consumption, sports activity, family history of breast cancer, ethnic group, body mass index, use of calcium supplements, hormone replacement therapy use, number of pregnancies, months of breast feeding, and age at first pregnancy (OR, 0.72; 95% CI, 0.57 to 0.90). Breast cancer risk did not change further if bisphosphonates were used for more years. Breast tumors identified in bisphosphonates users were more often estrogen receptor positive and less often poorly differentiated.
Conclusion: The use of bisphosphonates for longer than 1 year was associated with a 28% relative reduction in the risk of postmenopausal breast cancer. Tumors developing under bisphosphonates treatment tended to have a favorable prognostic factors profile.