Dec. 11, 2009 -- There might be link between a common osteoporosis treatment and a significantly reduced risk of breast cancer in women, according to two studies presented at the San Antonio Breast Cancer Symposium Thursday.
The first study from the Women's Health Initiative found that women who used bisphosphonates had 32 percent fewer cases of invasive breast cancer. The second, from a northern Israel study, found that women who used bisphosphonates for more than five years also had a 29 percent reduced risk of post-menopausal breast cancer.
Bisphophonates are drugs that can slow or stop the bone dissolving process that leads to osteoporosis. Popular examples of the medicines are drugs such as Fosamax, Boniva, Actonel and Reclast.
Dr. Richard Besser, ABC News' senior health and medical editor, said the lead researcher has a few theories about why the drugs could help reduce the risk.
"One is that these drugs could be toxic to the cancer cells themselves," Besser said on "Good Morning America."
"Another is that it could just interfere with the pathway by which women go on to develop breast cancer. But more work would need to be done in that area."
While experts are cautiously optimistic about the studies, several of them said that more information is necessary, and as of now, they would not suggest the use of bisphosphonates for women who do not have osteoporosis.
"These are very early studies showing a possible association, but without a good long-term follow-up," Dr. Sandhya Pruthi of the Mayo Clinic in Rochester, Minn., wrote in an e-mail. "However, bisphosphonates are drugs that also have side effects, so it is not something I would give to a patient who does not have osteopenia or osteoporosis to potentially prevent breast cancer at this time."
Besser agreed and advised women not to run out and buy osteoporosis treatments.
"These aren't ready for prime time," he said. "These studies were not done for this reason. So now they will do a big study and give half the women these drugs and another group of women not have these drugs and follow them over time to find out if it is truly protective."
But, Besser added, the findings hold hope.
"That's how some of the greatest discoveries come about, just by surprises like this," he said.
Bisphosphonates are "commonly used for the treatment of osteoporosis and for prevention and treatment of skeletal lesions due to malignancy," according to one of the studies' abstract descriptions.
Experts said they view the apparent breast cancer link as a favorable bonus to regular osteoporosis treatment.
"For women who need treatment for osteoporosis, these data suggest that there may be some secondary gain," Harold Burstein, breast oncologist at Dana-Farber Cancer Institute in Boston, said. "However, the data are not sufficient to suggest that bisphosphonate therapy would prevent breast cancer for ordinary women."
Data 'Should Justify' More Studies
Rather, one of the studies' greatest benefits could simply be increased interest in the positive effects of bisphosphonates, Burnstein said.
"The data should justify prospective studies to evaluate how important these interventions really are," Burnstein said.
The ABC News Medical Unit contributed to this report.