Breast Cancer Prevention Drug Risks Outweigh Benefits for Most Women

Benefits of tamoxifen varies among patients.

The serious side effect risks from a breast cancer drug outweigh the benefits the treatment provides in a majority of patients, a recent study indicates.

The study, published online in January 2015 in the Journal of the National Cancer Institute, finds that patients and their physicians need to make an informed decision regarding who may benefit from taking the drug tamoxifen, which has only been adopted by a small number of women eligible to take it.

"It's important because it highlights that the estimated benefit is not the same for all women, and so women need to go and have a very specific conversation with their providers about what their health looks like at that time, and whether this is a reasonable option for them," lead author Hazel Nichols, an assistant professor of epidemiology in the University of North Carolina Gillings School of Public Health, said in a press release.

The study noted that few women eligible to take tamoxifen to prevent breast cancer actually choose to take it, despite it having been shown to reduce the risk of invasive breast cancer. Meanwhile, American health experts have encouraged doctors to offer chemoprevention drugs to treat patients who face a higher breast cancer risk while also considered to face a lower risk for side effects.

Tamoxifen was initially approved in 1998 to treat women 35 years of age and older with those characteristics.

"Tamoxifen is very good at preventing breast cancer, but it also has to be weighed against an increased risk of uterine cancer, stroke, or blood clotting negative effects," Nichols said.

The researchers used a mathematical tool developed at the National Cancer Institute to evaluate the pros and cons of treatment in a group of 788 women taking tamoxifen without a prior history of breast cancer. The researchers took into account the patient’s age, race, breast cancer risk, and the risk carried by tamoxifen for serious side effects such as stroke, uterine cancer, and cataracts.

The study found that the benefits of tamoxifen outweighed the risks in 74% of the participants, but did not in 20% of the women. Participants who received hysterectomies before starting treatment with tamoxifen were found to be 11 times more likely to have a favorable risk-to-benefit profile.

Younger patients were also found to be more likely to benefit from tamoxifen, while African-American women were 65% less likely than Caucasian women to have greater benefits than risks from the drug.

Additionally, of the patients included in the study, 46% stopped taking tamoxifen before the end of the recommended 5-year treatment duration. Factors such as age, race, and breast cancer risk were not found to be strong predictors of which patients ceased treatment with tamoxifen early.

The results of the study illustrated that physicians and their patients should utilize tools that help them decide whether preventive drugs like tamoxifen are a viable option.

"I think we have seen that not all women who take tamoxifen for chemoprevention will have equivalent evidence that the risks outweigh the benefits, but the risk-benefit tool is easy to apply to estimate whether a woman's benefits are likely to outweigh the risks," she said.