Do bisphosphonates really decrease breast cancer risk?

Despite earlier observational studies, bisphosphonate treatment for 3 to 4 years appears not to decrease the risk of invasive postmenopausal breast cancer, according to a new study in JAMA Internal Medicine.

Led by researchers from the University of California, San Francisco, investigators used data from 2 randomized (1:1), double blind, placebo-controlled trials: the Fracture Intervention Trial (FIT) in which 6459 women aged 55 to 81 years were assigned to receive alendronate or placebo for a mean follow-up of 3.8 years and the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly-Pivotal Fracture Trial (HORIZON-PFT) in which 7765 women aged 65 to 89 years received annual intravenous zoledronic acid or placebo for a mean follow-up of 2.8 years. Women from either trial who had recurrent breast cancer or a history of breast cancer were excluded from analyses. Blinded review was conducted for each cancer adverse event report to verify incident invasive breast cancer cases.

No significant difference in the breast cancer rates was found in FIT: 1.5% (n = 46) in the placebo group and 1.8% (n = 57) in the alendronate group (hazard ratio [HR], 1.24, 95% confidence interval [CI], 0.84 to 1.83). Similarly in HORIZON-PFT, no significant difference was found in the rate of cancer in the placebo group, 0.8% (n = 29) and 0.9% (n = 33) in the zolendronic acid group (HR, 1.15, 95% CI, 0.70 to 1.89). When the data were pooled from FIT and HORIZON-PFT, no significant differences were found (HR, 1.20, 95% CI, 0.89 to 1.63).

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The researchers concluded that these findings do not support previous findings from observational research and that treatment with bisphosphonates for 3 to 4 years does not decrease the risk of invasive postmenopausal breast cancer.

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