A drug of a class commonly used to combat bone loss may reduce by a third the chance that some breast cancers will spread or recur, a large study has found.

While it may sound odd to treat cancer with a drug that acts on bone, evidence is accumulating that such drugs may do more than just prevent the loss of bone. Other studies are testing the drugs in patients with prostate or lung cancer.

The new study, published in Thursday’s New England Journal of Medicine, involved 1,803 premenopausal women with tumors that were fueled by estrogen. As part of their treatment, all received drugs that shut down their ovaries, preventing them from making estrogen, along with drugs that stymie cancer cells from using estrogen to grow.

Half also got the bone drug zoledronic acid, or Zometa, as an intravenous infusion twice a year for three years. Those who took the drug had a 36 percent reduction in cancer recurrences and metastases, compared with women who did not get it. After nearly four years, 54 women who received zoledronic acid and 83 who did not had a recurrence of their cancer or had a new cancer in the opposite breast or a metastasis to their bones.