drugs against osteoporosis may not protect women against breast cancer -
Osteoporosis drugs called bisphosphonates may not protect women against breast cancer as had been thought, according to a new study by researchers at UC San Francisco (UCSF).
The protective effect of drugs was widely accepted after several observational studies have shown that women who have them were less likely to have breast cancer.
But when the researchers evaluated the effect of two drugs most used osteoporosis - sold under brand names Fosamax and Reclast - in two large randomized clinical trials, drug or women protected by the breast cancer osteoporosis. The results were published August 11, 2014, in JAMA Internal Medicine .
The researchers said the link found in previous observational studies between taking drugs and having a lower incidence of breast cancer may be due to a third factor, low estrogen.
Since having low estrogen two weakens bones and protects against most breast cancers, the most likely women to be prescribed drugs for osteoporosis are generally also lower risk for cancer breast.
"They may have seen a lower risk of breast cancer in women using bisphosphonates in previous observational studies because these women had a lower risk of breast cancer to begin" said Trisha Hue, PhD, lead author of the study.
"post-menopausal women with osteoporosis usually have low estrogen levels," said Hue, an epidemiologist with the Centre coordination of San Francisco, a partnership between the CPMC and UCSF research Institute Department of epidemiology and Biostatistics. "the lower estrogen levels are strongly associated with a lower risk of breast cancer."
Steven Cummings, MD, co-author of the paper, a UCSF professor emeritus of medicine and director of the San Francisco coordinating Center, said women should not take these drugs thinking they will protect against the breast cancer.
"postmenopausal women should continue taking these drugs to prevent fractures, but they should not use bisphosphonates for prevention of primary breast cancer," said Cummings, Senior Investigator the research Institute CPMC.
data analyzed in the study come from two clinical trials, double-blind, placebo-controlled. in both trials, women who received bisphosphonates impacted slightly higher, but not statistically significant for breast cancer.
the Fracture Intervention trial (FIT) randomly assigned 6,459 US women 55 to 81 to alendronate or placebo for a follow average of 3.8 years, 1.8 percent of women who received the drug for breast cancer developed, while 1.5 percent of those who received placebo developed the disease
the health outcomes and impact reduced with zoledronic acid once a year-Pivotal Fracture Trial (HORIZON-PFT) randomly assigned to 7.765 US women, Canada, Asia, Europe and South America 65 to 89 at the annual zoledronic acid by intravenous or placebo for a mean follow-up of 2.8 years; 0.87 percent of women who received the drug for breast cancer developed, while 0.77 percent of those who received placebo developed the disease.
Women in both studies who had recurrent breast cancer or breast cancer reported history were excluded from the analysis.
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