New drug shown to reduce breast cancer in high-risk women

Eighty per cent of breast cancers occur in women over age 50. Preventative medications are available, but their potential for serious side effects has deterred women and their doctors from using them. Fortunately, the results of a new clinical trial suggest there may be a safer alternative. According to Dr. Eric Winquist, a scientist at Lawson Health Research Institute and Professor of Oncology at Western's Schulich School of Medicine & Dentistry, Exemestane can reduce the risk of developing breast cancer by 65 per cent amongst postmenopausal women.

Breast cancer is believed to thrive on estrogen. Available anti-estrogen medications have been shown to reduce the risk of breast cancer, but have also been associated with rare but serious uterine cancer and potentially fatal blood clots. Exemestane is an oral aromatase inhibitor that prevents the synthesis of estrogen and lowers the level of this hormone in the body. Since Exemestane provides the same powerful benefits as anti-estrogens without the serious toxicities.

A large randomized double-blind clinical trial called ExCel was launched to assess Exemestane as a breast cancer preventative . A total of 4,560 postmenopausal women from Canada, the United States, Spain, and France were enrolled, with London as the highest enrolling Canadian centre. Patients were split into two groups, one taking 25 mg of Exemestane and the other a matching placebo, once daily for five years. At three-years of follow-up, results indicated Exemestane reduced invasive breast cancers by 65 per cent. Patients taking Exemestane also developed fewer cases of precancerous breast findings known to have a higher risk of progressing to breast cancer.

Overall, Exemestane's side effect profile was excellent. Symptoms such as hot flashes, fatigue, sweating, insomnia, and joint paint were only slightly more common amongst women on Exemestane. However, that this did not affect patients' self-reports of overall health-related quality of life. More serious symptoms, such as bone fractures, osteoporosis, adverse cardiovascular events and other non-breast cancers, were equally common in both groups.

"Although the follow-up period is short at this point, these results have very exciting potential," Dr. Winquist says. "For postmenopausal women at a higher risk for developing breast cancer, Exemestane appears to be a highly effective drug therapy option with, on average, only mild side effects." Dr. Winquist is an investigator with Canada's NCIC Clinical Trials Group which led and coordinated the ExCel study. Moving forward, study participants receiving placebo will have the opportunity to receive Exemestane for five years.