Bisphosphonates May Not Protect Against Breast Cancer

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Bisphosphonates, such as alendronate, risedronate, ibandronate, pamidronate, and zoledronic acid, used to treat osteoporosis in postmenopausal women have been thought to reduce the risk of developing breast cancer; however, according to new research published in The Journal of the American Medical Association, that belief may not be true. Researchers at the University of California, San Francisco assessed whether alendronate or zoledronic acid would reduce the risk of breast cancer in two large clinical trials and they found that neither drug conferred protection.

In the alendronate study, 1.8% of women taking the drug developed breast cancer while 1.5% of those taking placebo developed the disease during an average follow-up period of nearly 4 years. In the zoledronic acid trial, 0.87% of those taking the drug and 0.77% of those taking placebo developed breast cancer during an average follow-up of about 3 years.

The researchers suggest that low estrogen, not bisphosphonates, lowered the incidence of breast cancer in postmenopausal women with osteoporosis in previous observational studies. Because those women naturally had low estrogen due to being postmenopausal, they already had a lower risk of developing breast cancer than women with normal estrogen levels. Researchers recommend that women with osteoporosis continue to take bisphosphonates to prevent fractures, but that they be aware that these drugs will not reduce their risk of developing breast cancer.

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Bisphosphonates may not protect women from breast cancer as had been thought.

Osteoporosis drugs known as bisphosphonates may not protect women from breast cancer as had been thought, according to a new study led by researchers at UC San Francisco (UCSF).

The drugs' protective effect was widely assumed after several observational studies showed that women who took them were less likely to get breast cancer.

But when researchers assessed the effect of two of the most widely used osteoporosis drugs – sold under the brand names, Fosamax and Reclast – in two large randomized clinical trials, neither drug protected women with osteoporosis from getting breast cancer. The results were published August 11, 2014, in JAMA Internal Medicine.


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