Bisphosphonates are medicines that help prevent bone loss and make bones stronger. Bisphosphonates are most often prescribed for postmenopausal women. A study found a strong association between taking oral (pills taken by mouth) bisphosphonates and a lower risk of breast cancer: women who took oral bisphosphonates were more than 30% less likely to develop invasive breast cancer compared to women who didn't take them. These results were reported at the 2009 San Antonio Breast Cancer Symposium.
The oral bisphosphonates are:
- Fosamax (chemical name: alendronate)
- Actonel (chemical name: risedronate)
- Boniva (chemical name: ibandronate)
Researchers looked at the medical records of 10,000 women in the long-term study called the Women's Health Initiative (WHI). The researchers compared the medical histories of the 2,216 women taking an oral bisphosphonate when they enrolled in the WHI to women who didn't take a bisphosphonate.
Compared to women who didn't take a bisphosphonate, women who did take an oral bisphosphonate were:
- 30% less likely to be diagnosed with invasive hormone-receptor-positive breast cancer; this reduction in risk was significant, which means the difference was likely because of the bisphosphonate and not just due to chance
- 31% less likely to be diagnosed with invasive hormone-receptor-negative breast cancer; this reduction in risk also was significant
- 41% more likely to be diagnosed with non-invasive ductal carcinoma in-situ (DCIS)
The increased risk of DCIS is surprising. Researchers think this unexpected result might have happened because the bisphosphonate slowed DCIS from progressing to invasive cancer, so less invasive cancer was diagnosed but more non-invasive DCIS was diagnosed.
A second study looked at breast cancer risk in 4,575 postmenopausal women, some of whom took an oral bisphosphonate for 5 or more years. Women who took a bisphosphonate had a 28% to 34% lower risk of invasive breast cancer. These results are comparable to the WHI study results.
While oral bisphosphonates can be taken for a number of years to strengthen bones, these studies found that they lowered breast cancer risk mostly during the first year they were taken, not during later use.
The researches also reported that when breast cancer did develop in women who took an oral bisphosphonate, the cancer had characteristics associated with a more favorable prognosis: HER2-negative and estrogen-receptor-positive, for example.
These studies looked at oral bisphosphonates. Other bisphosphonates are given intravenously:
- Aredia (chemical name: pamidronate)
- Bonefos (chemical name: clodronate)
- Boniva (chemical name: ibandronate)
- Reclast and Zometa (chemical name: zoledronic acid)
These intravenous bisphosphonates weren't included in the studies reviewed here, but it's likely that they also can lower breast cancer risk.
If you're a postmenopausal woman, your doctor may recommend a bisphosphonate to strengthen your bones or treat osteoporosis. These results and other research suggest that a bisphosphonate can lower your risk of developing invasive breast cancer in addition to improving bone health. Bisphosphonates need to be taken in a specific way and may cause serious side effects, so make sure you and your doctor discuss how to take the medicine.
Editor's note: In August 2014, 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 who’ve been diagnosed with osteoporosis. 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.