Two new studies suggest that women who take the drugs, called bisphosphonates, are about one-third less likely to develop breast cancer than women who do not.
One study, an analysis of data on over 150,000 women involved in the Women's Health Initiative, showed that there were 31% fewer cases of breast cancer among women who took Fosamax or other oral bisphosphonates than among women who didn't. Other commonly used oral bisphosphonates are Boniva and Actonel.
The second study, involving more than 4,000 postmenopausal women in Israel, showed that those who had breast cancer were 29% less likely to have taken oral bisphosphonates for at least one year than women who did not have breastcancer.
The two studies used different methods to arrive at the same basic result, adding to the strength of the findings, says Indiana University's Theresa Guise, MD, who moderated a news briefing on the findings at the San Antonio BreastCancer Symposium.
Still, the studies do not prove that the drugs prevent breast cancer, doctors here say. More definitive clinical trials in which half the women are given bisphosphonates and half are not and then they are followed over time to see how many in each group develop breast cancer should offer a clearer picture of the drugs' benefits within the year.
But "the idea that bisphosphonates may protect against breast cancer incidence is very exciting because there are about 30 million prescriptions for them written annually in the United States," says Rowan Chlebowski, MD, PhD, a medical oncologist at Harbor-University of California, Los Angeles Medical Center, who headed the new U.S. study.
"By protecting their bone health, women may also be protecting themselves against cancer," he tells WebMD.
Animal and lab research suggests that the drugs may fight breast cancer in a number of ways -- by directly killing tumor cells, by cutting off their blood supply, or by stimulating the immune system to mount an attack against the tumor, Chlebowski says.