A popular class of bone-building drugs known as bisphosphonates appear to significantly reduce women's risk of breast cancer, according to research presented Thursday at the San Antonio Breast Cancer Symposium.
In one study, researchers analyzed data from the huge National Institutes of Health-sponsored Women's Health Initiative and found that users of bisphosphonates had nearly a third fewer cases of breast cancer compared with nonusers. A second study involving more than 4,500 postmenopausal women in Israel with and without diagnoses of breast cancer found that those who reported using bisphosphonates for at least five years were about 30% less likely to receive a breast-cancer diagnosis, even after controlling for risk factors such as family history and use of other medications.
Low bone density had been linked with lower risk of breast cancer in previous studies, prompting scientists to look at data on women being treated with bisphosphonates for bone loss. But neither study presented Thursday was a clinical trial in which women were randomly assigned to take bisphosphonates or not. As a result, it still isn't definitive whether the drugs used to treat weak bones were actually responsible for the reduced risk of cancer. And why bisphosphonates appear to reduce breast-cancer risk isn't clear. Bisphosphonates have side effects, including bone and muscle pain as well as rare but serious cases of jaw bone death that have resulted in hundreds of lawsuits by plaintiffs alleging improper warnings about the drugs.
But the results provide the best evidence to date that the medicines appear to reduce women's risk of breast cancer. Still, it is too early for women to seek bisphosphonate therapy for the purpose of preventing cancer, said Gad Rennert, lead investigator of the Israeli study, which was sponsored by a U.S. private research foundation and several organizations in Israel. Bisphosphonates for treating osteoporosis include Merck & Co.'s Fosamax and Roche Holding AG's Boniva. Another bisphosphonate, Novartis AG's Zometa, is administered intravenously to prevent the spread of cancer into the bones of patients with a variety of cancers. Some 45 million prescriptions for bisphosphonates were written in the U.S. in 2008, according to data provider IMS Health.
In the analysis of the Women's Health Initiative data, researchers compared rates of breast cancer in 2,816 women who reported using oral bisphosphonates at the start of the study with 151,952 nonusers. The rate of invasive breast cancer was 3.3% in the bisphosphonate user group versus 4.4% among nonusers after an average of 7.8 years of follow-up. Moreover, the reduction wasn't related to the fragility of women's bones.
"Bisphosphonates may have direct inhibiting effects on breast cancer," Rowan Chlebowski, lead investigator on the study and an oncologist at Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, said of the results. But because bone is often a target of metastases -- spreading cancer cells -- for different kinds of tumors, the drugs have potential to work for other types of cancer as well, according to Dr. Rennert.
"Biology is usually smart," said Dr. Rennert, who also serves as director of the National Israeli Cancer Control Center and a professor at the Technion-Israel Institute of Technology. "If you have an agent that has anti-tumor qualities, it could be the case for other tumors, too. It has immense potential if [the result] holds."
By Shirley S. Wang, The Wall Street Journal
Reviewed / Posted by: Scott W. Yates, MD, MBA, MS, FACP
Reviewed / Posted by: Scott W. Yates, MD, MBA, MS, FACP
