Common osteoporosis drugs may decrease breast cancer risk

Women who take certain bone-building drugs used to prevent and treat osteoporosis may be at lower risk of breast cancer, according to a Hutchinson Center study recently published in the British Journal of Cancer.

The study found that women who used bisphosphonate drugs, such as Fosamax, Boniva and Zometa, for more than two years had a nearly 40 percent reduction in risk as compared to those who did not, according to lead author Dr. Polly Newcomb, head of the Cancer Prevention Program in the Public Health Sciences Division.

“This large study provides new evidence that the use of bisphosphonates is associated with a potentially important reduction in breast cancer risk,” Newcomb said.

The protective effect was observed only among women who were not obese. “Obese women may have elevated estrogen levels, so underlying hormones may influence the ability of bisphosphonates to reduce breast cancer risk,” said Newcomb, who is also a visiting scientist at the University of Wisconsin Carbone Comprehensive Cancer Center.

The way in which these drugs may prevent breast cancer is not known, but several research observations may be relevant. “These drugs may affect cell function and be important in cell growth and death – specifically the death of tumors or even premalignant disease,” Newcomb said. Researchers have found that some kinds of bisphosphonates directly cause cellular suicide, prevent tumors from establishing a blood supply, and inhibit the ability of cancer cells to bind to one another.

The study involved nearly 6,000 Wisconsin women, aged 20 to 69. Half had been diagnosed with invasive breast cancer and, for comparison purposes, half had not. The women were interviewed about their bone health—their history of fractures, whether they’d been diagnosed with osteoporosis and their history of bisphosphonate use.

Breast cancer risk factors such as first-degree family history of the disease, age at first birth, postmenopausal hormone use, and body mass index were accounted for in the analysis. “Because we were able to account for important cofounders, these findings may reflect real benefits due to the anti-tumor mechanisms of these medications,” the authors wrote.

The National Cancer Institute funded the study, which was conducted in collaboration with researchers at the University of Wisconsin Carbone Comprehensive Cancer Center.