The most important factors for determining risk of developing breast cancer are increased age, family history and having had a biopsy that showed signs of precancers, Nelson said.
One expert said he expected the report to stimulate a new look at this use of these medications.
"These drugs work, this is an effective chemoprevention regimen," said Robert Smith, senior director of cancer screening at the American Cancer Society in Atlanta.
Another reason that these drugs could be underused is that, as women age, they are more likely to see an internist or primary care physician than a gynecologist, and these types of doctors could be less likely to have a conversation about breast cancer chemoprevention, Smith said.
"The task force update is likely to stimulate some action among primary care physicians," Smith said.
Even though patients' concerns about side effects could also factor into the underuse of tamoxifen and raloxifene, most women do decide to take one of the drugs if their doctors recommend it, Smith said. The current report found that 70 percent of women took the recommended treatment dose.
The adverse effects of blood clots, endometrial cancer and cataracts are less likely if women take these drugs at a relatively young age, Nelson said. However, the risks might be too high for women who have a history of blood clots or cataracts, she added.
The reduced risk among young women "really does suggest that the period of time to actively assess risk and consider chemoprevention is not long after menopause" and even as women make the transition into menopause, Smith said.
Although the studies included in this report did not find a decrease in breast cancer mortality, it could be that it will take longer follow-up times to see a difference, Nelson said.
It could also be the fact that these drugs only reduce the risk of a type of breast cancer called hormone receptor-positive breast cancer and that survival is better for this type of breast cancer, Nelson said. Tamoxifen and raloxifene work by interfering with estrogen, which drives the growth of breast cancer in hormone receptor-positive cancers.
To learn more about breast cancer risk and the Gail model, visit the U.S. National Cancer Institute Breast Cancer Risk Assessment Tool.
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