Exemestane: A Promising New Option for Primary Prevention of Breast Cancer

CHICAGO—Women considered at risk for breast cancer developed fewer breast cancers and fewer precursor lesions by taking the aromatase inhibitor (AI) exemestane for 5 years, versus placebo, in a large Canadian study presented at the 2011 annual meeting of the American Society of Clinical Oncology.

 

“Our study not only showed an impressive reduction in breast cancers, but also an excellent side effect profile,” said Paul Goss, MD, PhD, Professor of Medicine at Harvard Medical School, Boston. Goss noted that currently approved drugs for preventing breast cancers—tamoxifen and raloxifene—are associated with the potential for rare but serious side effects, including venous thromboembolism, that many women consider unacceptable.

 

Exemestane is currently approved for the treatment of estrogen receptor–positive breast cancer in postmenopausal women. It is not approved for prevention.

 

This study, the National Cancer Institute of Canada Clinical Trials Group MAP.3, is the first randomized trial to assess an AI for breast cancer prevention in healthy women. The study enrolled 4560 women from 4 countries who had at least 1 of the following risk factors: age ≥60 years, 5-year Gail risk score >1.66%, previous atypical ductal or lobular hyperplasia or lobular carcinoma in situ, or ductal carcinoma in situ (DCIS) with prior mastectomy.

 

Simply being aged 60 years or older—which accounts for about half the population—qualified a woman as being at risk for breast cancer, he noted.

 

At a median follow-up of 3 years, the group receiving exemestane had a 65% reduction in invasive cancers (11 occurred in the exemestane group vs 32 in the placebo group). There was also a 60% reduction of invasive breast cancer and pre-invasive DCIS, and fewer cases of cancer precursor lesions, such as atypical ductal hyperplasia and atypical lobular hyperplasia, with exemestane, Goss reported.

 

“We believe that the results from the MAP.3 trial indicate that exemestane is a promising new option for preventing breast cancer in menopausal women,” he said.

 

This study was supported by the Canadian Cancer Society; Pfizer Inc. PEG supported in part by the Avon Foundation.