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Two Studies Show Bisphosphonates Don’t Reduce Breast Cancer Risk

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Bisphosphonates are medicines that help prevent bone loss and make bones stronger. Bisphosphonates are usually prescribed for postmenopausal women diagnosed with osteoporosis or who have weak or thinning bones.

In studies looking at the effectiveness of bisphosphonates to treat osteoporosis, the researchers noticed that women who were taking a bisphosphonate seemed to have a lower risk of breast cancer compared to women who weren’t taking a bisphosphonate. But these observations needed to be tested in studies looking specifically at bisphosphonates and breast cancer risk.

An analysis of two randomized studies found that 3 to 4 years of treatment with either Fosamax (chemical name: alendronate sodium) or intravenous zoledronic acid doesn’t seem to reduce breast cancer risk in postmenopausal women.

The analysis was published online on Aug. 11, 2014 by JAMA Internal Medicine. Read the abstract of “Effect of Bisphosphonate Use on Risk of Postmenopausal Breast Cancer: Results From the Randomized Clinical Trials of Alendronate and Zoledronic Acid.”

The analysis looked at two studies:

  • the Fracture Intervention Trial (FIT)
  • the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly-Pivotal Fracture Trial (HORIZON-PFT)

FIT randomly assigned 6,459 postmenopausal women ages 55 to 81 to take either:

  • a daily Fosamax pill
  • a daily placebo pill (a sugar pill that looked just like the Fosamax pill)

for 4 years. All the women had been diagnosed with osteoporosis.

The women were followed for about 4 years after that.

HORIZON-PFT randomly assigned 7,765 postmenopausal women ages 65 to 89 to get either:

  • an IV infusion of zoledronic acid
  • an IV infusion of a placebo solution (a solution that looked just like the zoledronic acid)

once a year for 3 years. All these women also had been diagnosed with osteoporosis.

The women were followed for about 3 years after that.

The researchers then compared breast cancer rates in women who got either Fosamax or zoledronic acid to breast cancer rates in women who got a placebo. The percentages of women diagnosed with breast cancer in each study were:

  • FIT:
    • 1.8% of women taking Fosamax
    • 1.5% of women taking the placebo
    • 0.9% of women getting zoledronic acid
    • 0.8% of women getting the placebo

These very small differences weren’t statistically significant, which means they could have been due to chance and not because of the difference in treatment. There were also no differences when the information from the two studies was combined.

“These data provide evidence that 3 to 4 years of treatment with bisphosphonate -- alendronate or zoledronic acid -- therapy does not reduce the risk of incident breast cancer in postmenopausal women,” the researchers wrote. “The discrepancy between our results and the reports of associations in observational studies may be an example of indication bias and illustrates the limitation and hazard of drawing conclusions about treatment effects from observational studies (even those that are very well done) and emphasizes the value of confirming such associations in randomized trials."

While these results are disappointing, the researchers said that more studies looking at breast cancer risk and bisphosphonates in women who don’t have osteoporosis should be done. It may be that bisphosphonates help reduce risk in women with strong bones.

If you're a postmenopausal woman, your doctor may recommend a bisphosphonate to strengthen your bones or treat osteoporosis. Bisphosphonates need to be taken in a specific way and may cause serious side effects. If you're prescribed a bisphosphonate, make sure you and your doctor talk about how to take the medicine.

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