Highlights from: 42nd Annual Meeting of the American Society of Clinical Oncology.

A long-term analysis from a large-scale international clinical trial indicates that postmenopausal women with early breast cancer who were switched to exemestane (Aromasin, Pfizer) after two or three years of tamoxifen therapy (Nolvadex, Astra Zeneca) experienced a significant improvement in survival and a marked reduction in the risk of breast cancer recurrence and metastasis compared with women who continued taking tamoxifen. These findings were concluded from the first mature analysis of the Intergroup Exemestane Study, a randomized trial begun in 1998. The study enrolled 4,724 women from 37 countries. All of these patients had been treated for early breast cancer and had been disease-free after two to three years of tamoxifen treatment. Upon entry into the trial, the women were selected to switch to exemestane for an additional two or three years to complete five years of treatment or to continue with tamoxifen for a total of five years of treatment. At a median follow-up of 4.8 years, an analysis was carried out in two groups of patients. An intent-to-treat (ITT) group included 122 patients with unknown estrogen receptor (ER) status; these patients were later found to be ER-negative, and the analysis was repeated to exclude the ER-negative patients. Overall, in the ITT population, there were 808 first events: 354 in the exemestane group and 454 in the tamoxifen group. Those using exemestane had a 24% lower risk of experiencing any first event, a 44% lower incidence of cancer in the contralateral breast, and a 17% reduction in the risk of metastasis, thus resulting in improved disease-free survival. In addition, women receiving exemestane had a 15% lower risk of dying of any cause than the women who continued using tamoxifen, thereby leading to improved overall survival. Although there were no significant differences between the two treatment groups in terms of myocardial infarction, angina, or stroke, those continuing tamoxifen treatment tended to have more thromboembolic events (blood clots) and serious gynecologic events (uterine cancer, polyps, and vaginal bleeding). By contrast, patients receiving exemestane had a slightly higher number of bone fractures, a consequence that points to the need for bone density monitoring during exemestane therapy.