Breast cancer risk slashed by hormone-blocking pill, study shows

(CBS/AP) There's a new option for millions of women at high risk for breast cancer. A drug called Aromasin more than halved the likelihood of developing breast cancer, without the side effects that have tempered enthusiasm for other drugs, a new study showed.

It was the first time that Aromasin, Femara, Arimidex, and other aromatase inhibitors were tested in healthy women. These hormone-blocking pills are used now to block recurrence of breast cancer post-menopausal patients, and doctors have long thought they might help prevent the disease in the first place.

Prevention drugs aren't advised for women at average risk of breast cancer. Those with gene mutations or other factors that put them at high risk have two choices for prevention - tamoxifen and raloxifene. But these drugs are unpopular because they can cause uterine cancer, blood clots and other problems.

"Here's a third breast cancer prevention drug that may in fact be safer," said Dr. Allen Lichter, chief executive of the American Society of Clinical Oncology.

The study - discussed Saturday at the society's annual meeting in Chicago - involved 4,560 women. All had at least one risk factor - being 60 or older, a prior breast abnormality or pre-invasive cancer, or a high score on a scale that takes into account family history and other things.

They were given daily doses of Aromasin (exemestane) or dummy pills. After about three years, there were 11 cases of invasive breast cancer among those on the drug versus 32 among the others. That worked out to a 65 percent reduction in risk for those on the drug - enough of a benefit that scientists decided that all participants should be offered it.

Major side effects, such as broken bones, high cholesterol and heart problems, were similar in both groups. Slightly more women on the drug reported hot flashes, fatigue, sweating, insomnia and joint pain, but quality-of-life scores were similar.

The study's leader, Dr. Paul Goss of Massachusetts General Hospital, figured that 26 women would need to take exemestane for five years to prevent one case of breast cancer. Even though this study did not compare the drug to tamoxifen, previous studies suggested 96 women would need to take it for five years for each breast cancer prevented.

"This is a new option for prevention of invasive breast cancer for a wide pool of women," Goss said.

Still, it could be a tough sell. These women have only about a 2 percent to 3 percent risk, individually, of being diagnosed with breast cancer in the next five years. A prevention pill that cuts that chance by 65 percent means a roughly 1 percent risk, said Dr. Eric Winer, breast cancer chief at Boston's Dana-Farber Cancer Institute.

"Many women are not willing to take a daily medicine" for such a small risk, he said.

The "New England Journal of Medicine" published results of the study, which was paid for with help from the Canadian Cancer Society, Pfizer, and the Avon Foundation. Goss and some other researchers have been paid speakers for Pfizer and other cancer drug makers.

Brand-name aromatase inhibitors cost $340 to $420 a month, though some are available as generics.

Worldwide, about 1.3 million women are diagnosed with breast cancer each year and nearly 500,000 women die of the disease. Last year in the U.S., there were about 207,000 new cases and 40,000 deaths from breast cancer.

The National Cancer Institute has more on breast cancer.