Aromatase inhibitors like anastrozole and letrozole seem to protect breast cancer survivors from recurring malignancies, according to two independent controlled trials. In one large-scale study, investigators gave placebo or letrozole to more than 5,000 women with early-stage breast cancer who had already taken tamoxifen for 5 years. About 2 1/2 years into the trial, only 75 woman in the letrozole group had a recurrence or a new primary tumor in the contralateral breast, compared to 132 in the placebo group. The dramatic results prompted researchers to stop the trial. Adverse effects of the aromatase inhibitors included hot flashes, as well as joint and muscle pain.1 The risk of osteoporosis may also have been slightly greater in the letrozole group.
Italian researchers obtained similar results using anastrozole, presenting their results only a few weeks ago at the San Antonio Breast Cancer Symposium. In that trial, postmenopausal women who had estrogen receptor-positive breast cancer and had been taking 20 mg of tamoxifen daily for 2 or more years either continued on the drug for a total of 5 years or were switched to 1 mg/day of the aromatase inhibitor for the rest of the 5-year period. Among the 426 women enrolled in the study, 26 either died, had a recurrence, or a new primary tumor while on tamoxifen, versus 10 in the anastrozole group. Put another way, anastrozole cut the risk of cancer recurrence by 64% (hazard ratio: 0.36, 95% CI 0.17 0.75, P = 0.006) and the risk of dying by 82%. Serious side effects were more common in the tamoxifen group.2
1. Goss PE, Ingle JN, Martino S, et al. A randomized trial of letrozole in postmenopausal women after five years of tamoxifen therapy for early stage breast cancer. N Engl J Med. 2003;349:1793-1802.
2. Boccardo F, Rubagotti F, Amoroso D, et al. Anastrozole appears to be superior to tamoxifen in women already receiving adjuvant tamoxifen treatment. Paper presented Wednesday. December 3, 2003. (www.abstracts2view.com/bcs03)