Recent observational studies have suggested that bisphosphonates may protect women from breast cancer, but this theory has not been tested in randomized trials—until now. Researchers assessed the effects of the 2 most widely used osteoporosis drugs—alendronate (Fosamax) and zoledronic acid (Reclast)—and determined that neither drug protected women with osteoporosis from developing breast cancer. Study findings were published August 11 online ahead of print in JAMA Internal Medicine.
“They may have seen a lower risk of breast cancer in women using bisphosphonates in the earlier observational studies because those women had a lower risk of breast cancer to begin with,” said lead author Trisha Hue, PhD, an epidemiologist with the San Francisco Coordinating Center, Department of Epidemiology and Biostatistics, at the University of California, San Francisco. Dr. Hue and her coinvestigators believe that the link found in the previous observational studies between taking the drugs and having a lower incidence of breast cancer may be due to low estrogen levels in the women studied.
Trisha Hue, PhD
Data analyzed in this study came from 2 large randomized, double-blind, placebo-controlled clinical trials—The Fracture Intervention Trial (FIT) and the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly Pivotal Fracture Trial (HORIZON-PFT). In both trials, women who received bisphosphonates had a slightly higher but statistically nonsignificant incidence of breast cancer.
FIT randomly assigned 6,459 women aged 55 to 81 years from the United States to alendronate or placebo for an average follow-up of 3.8 years. No significant difference in the rate of breast cancers was seen: Fifty-seven women (1.8%) who received the drug developed breast cancer, while 46 (1.5%) of those given placebo developed the disease.
HORIZON-PFT randomly assigned 7,765 women aged 65 to 89 years from the United States, Canada, Asia, Europe, and South America to annual intravenous zoledronic acid or placebo for an average follow up of 2.8 years. Results showed that 33 women (0.9%) who received the drug developed breast cancer and 29 (0.8%) women given placebo developed the disease.
Women in either study who reported a history of breast cancer or who had recurrent breast cancer were excluded from the analyses.
“These two randomized clinical trials do not support the findings from observational research,” Dr. Hue and colleagues reported. “Contrary to the results from observational studies, we found that 3 to 4 years of bisphosphonate treatment did not decrease the risk of invasive postmenopausal breast cancer.”