Osteoporosis Drugs Good for Bones but Not Breast Cancer Prevention

Contrary to previous observational studies, bisphosphonates do not protect women from breast cancer, according to the results of a new study published in JAMA Internal Medicine.

While previous observations have linked the use of drugs such as alendronate (Fosamax) and zoledronic acid (Reclast) to a reduced risk of breast cancer, researchers at UC San Francisco found no protective effect when they conducted a randomized controlled clinical trial.

Pertinent Points

-Osteoporosis drugs such as Fosamax (alendronate) and Reclast (zoledronic acid) do not reduce the risk of breast cancer, as some observational studies had previously indicated.

- Bisphosphonates are not responsible for preventing breast cancer. Instead, low estrogen levels may be responsible for the previous, misleading observed association between bisphos-phonate use and reduced breast cancer risk.

The new research suggests that the previous, misleading finding may have mistakenly associated a lower risk of breast cancer with bisphosphonate use because women taking the drugs already were less likely to have low levels of estrogen. Since having low estrogen is known to weaken bones, the UC San Francisco team speculates that the previous observational studies failed to account for the fact that the women most likely to be prescribed drugs for osteoporosis were already at a lower risk for breast cancer. Low estrogen is also known to protect against breast cancer, the authors noted.

Clinically, women should continue to take bisphosphonates for osteoporosis to prevent fractures, but the authors said the drugs should not be given to prevent breast cancer, the authors said.

In the latest study, the researchers analyzed data from two placebo controlled clinical trials. While in both trials the women who received bisphosphonates had a slightly higher incidence of breast cancer, the findings were not statistically significant.

In the first trial, involving nearly 6,500 women, 1.8% of women taking the drug developed breast cancer, while 1.5% receiving the placebo developed breast cancer. In the second trial, involving 7,765 women, 0.87% of the women given the drug developed cancer, while 0.77% of those given the placebo did.