‘A promising new way to prevent breast cancer’

A large, randomized double-blind study led by the National Cancer Institute of Canada’s Clinical Trials Group found the aromatase inhibitor exemestane reduces the risk of breast cancer by 65 percent in high risk, postmenopausal women, compared with placebo.

Dr. Anne McTiernan of the Public Health Sciences Division contributed to the study findings. McTiernan directs the Seattle ExCel study clinical site, based at the Hutchinson Center. The Seattle site recruited nearly 400 study participants, the second-highest number enlisted.

“Our results indicate that exemestane is a promising new way to prevent breast cancer in menopausal women most commonly affected with breast cancer,” said Harvard Medical School’s Dr. Paul Goss, lead study author. He presented the ExCel study findings on June 4 at the 2011 annual meeting of the American Society of Clinical Oncology in Chicago. The study results were published the same day in The New England Journal of Medicine.

Goss said the more than 4,500 study participants taking exemestane appeared to experience fewer aggressive tumors and few side effects from taking the drug. However, he cautioned that the study participants have only been followed for an average of three years.

Importance of ExCel study

Two breast cancer prevention drugs, tamoxifen and raloxifene, are approved for women at high risk. However, due to rare but potentially fatal side effects, only 4 percent of high-risk women take tamoxifen. Thus, effective and safer options for breast cancer prevention are needed.

The ExCel study is the first randomized trial to assess an aromatase inhibitor as a breast cancer preventative in healthy women. Exemestane is already used to prevent breast cancer recurrence because it blocks the body from producing estrogen. Without estrogen, breast cancer cells cannot survive. Earlier findings showed that exemestane was able to halt the occurrence of new cancers in the unaffected breasts of women who have already had breast cancer.

The study participants reported symptoms such as hot flashes, fatigue, sweating, insomnia and joint pain; these complaints were slightly more common in the women taking the study medication. However, these symptoms did not appear to affect self-reports of overall health-related quality of life. More serious adverse events were equal in both groups.

The NCIC Clinical Trials Group, based at Queen’s University in Kingston, Ontario, led ExCel study sites throughout Canada, the U.S. and Spain.

The Canadian Cancer Society Research Institute, the Canadian Institutes for Health Research, Pfizer and the Avon Foundation funded the study.

[Adapted from an ASCO news release]