The drugs work by blocking the effects of estrogen in breast tissue, lowering the chance of hormone-related cancers. But they also increase the risk of blood clots and hot flashes, among other side effects – so they shouldn’t be handed out to everyone, the U.S. Preventive Services Task Force (USPSTF) said in its new draft guidelines.

“Currently only a minority of women for whom the medication might be indicated are actually taking it,” said Dr. Mark Ebell, a member of the Task Force from the University of Georgia College of Public Health in Athens.

“I don’t think there’s a right or wrong answer for women,” he told Reuters Health. “The main thing is just for women to be aware of this as an option and to talk to their doctor if they think they might be at increased risk.”

Women are considered at high risk if they have a five-year chance of developing breast cancer of at least one in 60. Tools such as the Gail model (https://1.usa.gov/6eW4G) take into account a woman’s age, race, personal history of breast exams and family history of cancer to estimate her own risk of breast cancer.

A review conducted for the USPSTF and published concurrently found tamoxifen (marketed as Nolvadex and Soltamox) and raloxifene (Evista) decreased women’s chances of developing breast cancer by 30 to 56 percent.

Both drugs also doubled the risk of blood clots and tamoxifen increased the chance of endometrial cancer and cataracts, according to findings published in the Annals of Internal Medicine.

The review did not include studies that focused on women with breast-cancer related BRCA gene mutations.

Angie Fagerlin, a bioethicist from the University of Michigan Medical School and the Ann Arbor VA, said it’s important to consider an approximately 50-percent relative reduction in breast cancer risk in context.

For a woman who starts out with a one in 40 chance of developing cancer, she told Reuters Health, “Your risk goes from 2.5 to 1.25 (percent). It’s a 1 percent difference in your risk of breast cancer, having to take a drug every day for five years that has some side effects.”

But for some women who have a much higher short-term risk of breast cancer – as high as 16 percent – the drugs are more likely to be worth potential side effects, said Fagerlin, who wasn’t involved in the new review or the Task Force decision.

“There are a lot of things that play into this decision,” she said. “Women should know that this is an option, and they should be told their risks and benefits in a way they can understand.”

˜TAKE A TEST RUN’

About one in 8 women will be diagnosed with breast cancer during her lifetime and one in 36 will die of the disease, according to the American Cancer Society.

The new draft recommendations echo guidelines released by the Task Force a decade ago but now have more evidence behind them, according to Ebell. They will be posted for public comment until May 13 here: https://bit.ly/cy0SzP.

Other doctor groups, including the American Society of Clinical Oncology, also recommend some women at high risk of breast cancer be offered tamoxifen or raloxifene.

Elissa Ozanne, who studies decision science at the University of California, San Francisco, said the most common problems reported with tamoxifen and raloxifene include hot flashes and other “quality-of-life” side effects.

“The serious ones are very rare,” Ozanne, who wasn’t involved in the new research, told Reuters Health. If women are worried about side effects and how they might feel on the drugs, she added, “It’s something that they could try out and take a test run of it.”

Generic tamoxifen can be bought for about $100 per month or less.

Ozanne pointed out that research suggests women can reduce their risk of breast cancer through lifestyle changes, as well as medication.

“There are a lot of things women can think about doing, and tamoxifen is one of them, and so are things like maintaining a healthy body weight,” she said.

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