Technology Science - Drug prevents breast cancer in some women: study

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A drug discovered in the 1990s has been shown to reduce the risk of breast cancer in women at high risk of developing the disease, without the side effects of other prevention drugs, a major study has found.

More than 23,000 women were diagnosed with breast cancer last year in Canada.More than 23,000 women were diagnosed with breast cancer last year in Canada. (CBC)

It was the first test in healthy women of hormone-blocking pills called aromatase inhibitors. They're used now to prevent recurrences in breast cancer patients who are past menopause, and doctors have long suspected they may help prevent initial cases, too.

Prevention drugs aren't advised for women at average risk of breast cancer. Those at higher risk because of gene mutations or other reasons already have two choices for prevention â€Â" tamoxifen and raloxifene. But these drugs are unpopular because they carry small risks of 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 was discussed Saturday at the society's annual meeting in Chicago, along with another one that could change care for thousands of women each year with breast cancer that has spread to lymph nodes. It found that giving radiation to the armpit â€Â" not just the breast â€Â" after surgery significantly lowered the chances the cancer would come back.

The prevention study, published online by the New England Journal of Medicine, involved 4,560 women from the U.S., Canada, Spain and France. They had at least one risk factor â€Â" 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 the medication exemestane, sold under the brand name Aromasin, or a placebo. 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 per cent reduction in risk for those on the drug â€Â" enough of a benefit that independent monitors decided all participants should be offered it.

Serious 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.

Tough sell

Earlier studies of aromatase inhibitors found they can cause bone loss, vaginal dryness, problems having sex, joint pain and muscle aches, so it will take longer study to see if these occur, Lichter said.

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 a single 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," without the serious side effects of tamoxifen or raloxifene, Goss said.

Still, it could be a tough sell. These women have only about a two per cent to three per cent risk, individually, of being diagnosed with breast cancer in the next five years. A prevention pill that cuts that chance by 65 per cent means they'll have about a one per cent risk, said Dr. Eric Winer, breast cancer chief at Dana-Farber Cancer Institute in Boston.

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

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

The Canadian Cancer Society, Pfizer and the Avon Foundation helped pay for the study. Goss and some other researchers have been paid speakers for Pfizer and other cancer drug makers.

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