Osteoporosis drug cuts risk of breast cancer, study finds

A widely used osteoporosis drug is safer and just as effective at reducing the risk of invasive breast cancer as tamoxifen, the only drug currently approved for that use, according to data released Monday from an eagerly awaited trial of nearly 20,000 postmenopausal women.

After an average four years of treatment, both raloxifene and tamoxifen reduced women’s risk of invasive breast cancer by about 50 percent, say researchers with the Study of Tamoxifen and Raloxifene, or STAR.

But there were 36 percent fewer uterine cancers and 29 percent fewer blood clots among women taking raloxifene compared with those on tamoxifen.

“The data are very gratifying,” said Norman Wolmark, chairman of the National Surgical Adjuvant Breast and Bowel Project, which coordinated the trial.

STAR randomly assigned 19,747 postmenopausal women deemed to be at increased risk of breast cancer to take either tamoxifen or raloxifene for five years.

An estimated half-million postmenopausal U.S. women already take raloxifene, marketed as Evista, for osteoporosis, says the National Cancer Institute, the sponsor of STAR. A large clinical trial that led to Evista’s approval in 1997 showed it reduced the incidence of breast cancer as well as osteoporosis. Although Evista is not yet approved for reduction of breast cancer risk, doctors could prescribe it for that purpose.

Tamoxifen has been prescribed for more than 20 years to reduce the risk of a recurrence in breast cancer patients. In 1998, the drug won Food and Drug Administration approval for reducing the chance of breast cancer in healthy women deemed to be at increased risk of developing the disease.

Simply being 60 or older places women in the increased-risk category. Wolmark, chairman of oncology at Allegheny General Hospital in Pittsburgh, says an estimated 8 million U.S. women are eligible to take tamoxifen for risk reduction, “yet a tiny fraction” do.

“I think women were generally concerned about the serious side effects,” Wolmark said.

While STAR found raloxifene and tamoxifen were equally effective in preventing invasive breast cancer, women taking the osteoporosis drug were 40 percent more likely to develop ductal carcinoma in situ or lobular carcinoma in situ, non-invasive cancers that do not spread beyond the breast.

“I think that has to be weighed in the decision-making process,” Wolmark said, noting that only about 8 percent of women with non-invasive breast cancers develop invasive tumors.

In a statement, Len Lichtenfeld, deputy chief medical officer for the American Cancer Society, said raloxifene’s lack of protection against non-invasive breast cancer complicates matters. “The outcome of the study is not as clear cut as we might have hoped for,” Lichtenfeld said. “It will take some time for experts to review the data to determine which of the two treatments is preferable.”