Bisphosphonate drugs for osteoporosis may offer protection from breast cancer

December 09, 2009

Women who took a commonly used class of osteoporosis drugs called bisphosphonates had significantly fewer invasive breast cancers than women not using the bone-strengthening pills, according to a new analysis of data from the Women's Health Initiative (WHI). The analysis from a segment of the more than 150,000 generally healthy post-menopausal women in the WHI study found that those taking Merck & Co's Fosamax, or other bisphosphonates, had 32 % fewer cases of invasive breast cancer than women who did not use the osteoporosis medicines, researchers found. The study was headed by Dr. Rowan Chlebowski, chief oncologist from the Los Angeles Biomedical Research Institute. The latest findings from this observational study were presented at the San Antonio Breast Cancer Symposium on Thursday.

The impetus for looking at the connection between bisphosphonates and breast cancer came from data from a clinical trial in which breast cancer patients who were given Novartis' bisphosphonate Zometa intravenously every six months had fewer contralateral breast cancers, Chlebowski explained. "It appeared to make bone less hospitable to breast cancer," Chlebowski said. Contralateral breast cancer is typically a second new case of cancer in the other breast, rather than the spread of the originally detected breast cancer.

Studying 2,816 participants who were using bisphosphonates when they entered the WHI program, researchers found that only 64 women developed breast cancer. That translates into 32 % fewer breast cancers in women using bisphosphonates compared with women who did not use them, researchers said.

"Bisphosphonates reduce angiogenesis (flow of blood and nutrients to the tumor) and stimulate immune cells responsible for tumor cell surveillance as potential mediators," Chlebowski said. "This association needs to be studied further." Researchers cautioned that this was an observational study that does not necessarily carry the same scientific weight as a blinded clinical trial. However, they said, several ongoing breast cancer trials evaluating oral and intravenous bisphosphonates will be available in the near future to provide randomized clinical trial evidence regarding their influence on new contralateral breast cancer risk.