Osteoporosis Drug Shows "Promise" in Treatment of Breast Cancer

A class of drugs known as bisphosphonates, already used to prevent osteoporosis in women after menopause, appears to have an additional and unexpected benefit: a lower overall incidence of breast cancer. There was also a hint in the studies that bisphosphonates could affect a particular type of tumor that is notorious for its resistance to treatment: tumors that are not fueled by the hormone estrogen.

The results of the study, which was based on a review of data collected as part of the ongoing Women's Health Initiative, involved 151,592 postmenopausal women followed on average for 7.8 years. Among them were 2,216 who happened to be taking oral bisphosphonates for osteoporosis when they entered the study.

The "raw" data found 3.29 new cancers per 1,000 women per year among those taking bisphosphonates versus 4.38 cancers per 1,000 women per year among those not taking the drugs. After the data was "smoothed" (adjusting for different risk factors such as age and medical history) a repeat analysis determined that there were 32% fewer new breast cancers among those taking bisphosphonates.

Dr. Rowan T. Chlebowski, a cancer researcher at Harbor-U.C.L.A. Medical Center and the author of the study, said the drugs might act by having a direct toxic effect on tumor cells or could disrupt conditions favoring tumor growth at the cellular level.

Other cancer researchers and clinical specialists stated that the findings related to bisphosphonates were "of considerable interest" but that further research will be necessary in order to learn precisely how bisphosphonates exert their anti-tumor properties and that it could be "several years" before these drugs will become a standard part of breast cancer therapy.

The findings, released during Thursday's sessions of the San Antonio (TX) Breast Cancer Symposium, indirectly support the results of a similar analysis published in this year's February 12^th edition of the New England Journal of Medicine. That report cited evidence that another bisphosphonate, zoledronic acid, seems to be effective as an addition to current chemotherapy of breast cancer such as tamoxifen

In the United States, bisphosphonates are available as the brand name drug Fosamax and in generic form as alendronate sodium.