Photo of woman taking a breast exam
Women at high risk for breast cancer are needed to evaluate a drug that may help prevent the disease. The drug, exemestane, is being studied at UC Davis Medical Center as part of a national clinical trial sponsored by the National Cancer Institute of Canada.

Healthy, postmenopausal women at increased risk for breast cancer may be eligible to participate in a major international study to determine whether the drug exemestane can prevent the disease. The ongoing study is sponsored by the National Cancer Institute of Canada.

“Exemestane may present a new breakthrough in the prevention of breast cancer, and has the potential to greatly decrease the risk of this deadly disease, with fewer side effects than currently available preventive medications,” said John Robbins, professor of general medicine at UC Davis School of Medicine and principal investigator of the UC Davis arm of the study.

Exemestane is one of a new class of anti-cancer medications known as aromatase inhibitors. Aromatase inhibitors have shown promise in preventing breast cancer recurrences in women previously treated for the disease, but have not yet been clinically studied as a way to prevent breast cancer in high-risk women. The current study is the first designed to answer this question.

The drug tamoxifen has already been shown to prevent breast cancer in high-risk women, but many women have found its side effects, including the risk of blood clots and endometrial cancer, unacceptable. Preliminary research suggests that exemestane will have fewer side effects than tamoxifen.

For the purposes of the study, women are considered at increased risk of developing breast cancer if they have a strong family history of breast cancer, have had a prior breast biopsy, or are age 60 or older, among other factors. All participants must be postmenopausal, at least 35 years old, have no history of invasive breast cancer and using no hormone replacement therapy.

Study volunteers will be randomized into one of two groups. In the first group, participants will receive oral exemestane daily for five years. In the second group, patients will receive an oral placebo daily for five years. The study is “double-blind,” meaning that neither the participants nor the study investigators will know who is taking the placebo until after the study is over.

According to the  American Cancer Society, a woman in the United States has a 1-in-7 lifetime chance of developing invasive breast cancer, up from 1-in-11 odds in 1975.