Evidence Of Osteoporosis Drugs' Breast Cancer Prevention ‘Misleading'

A new analysis of clinical trial data by a researcher team at the University of California, San Francisco suggests that earlier evidence linking use of osteoporosis drugs and successful breast cancer prevention was misleading.

According to the researchers, assessment of several observational studies showing that women who took Fosamax and Reclast/Zometa were less likely to develop breast cancer may actually be due to another factor – low estrogen.

Known as bisphosphonates, Fosamax and Reclast/Zometa are drugs given to osteoporotic patients. In 2011, the drugs were given to women undergoing treatment for breast cancer as a standard of care. A previous study reported that Reclast/Zometa lowered the risk of death from breast cancer in women by 37 percent after taking the drug at six-month intervals for three years. A connection between low estrogen and treatment with Zometa in breast cancer patients was also made in the study. A 2009 study also indicated that Fosamax along with other bone drugs may cut the risk of breast cancer in older women.

Now however, the UCSF researchers reported that administering the osteoporosis drugs did not protect the women from developing breast cancer. Low estrogen levels, which weakens bones, already protects women from most forms of breast cancer and therefore lowered osteoporotic women’s risk of developing breast cancer.

“They may have seen a lower risk of breast cancer in women using bisphosphonates in the earlier observational studies because those women had a lower risk of breast cancer to begin with,” said Dr. Trisha Hue, lead author of the study. Data analyzed in the study were taken from two clinical trials in which women who took the bone drugs had a slightly higher but statistically non-significant incidence of breast cancer.

The UCSF scientists warned against taking the bone drugs mainly for breast cancer protection instead of osteoporosis. Steven Cummings, co-author of the paper and UCSF emeritus professor of medicine said, “Post-menopausal women should continue taking these drugs for the prevention of fractures, but they should not use bisphosphonates for the prevention of primary breast cancer.”

The scientists published their findings in this week’s edition of JAMA Internal Medicine.