Exemestane Shows Advantage Over Tamoxifen for Metastatic Breast Cancer

Paula Moyer, MA

March 19, 2004

March 19, 2004 (Hamburg, Germany) — The first head-to-head phase III trial of an aromatase inhibitor against tamoxifen shows that exemestane has benefits over tamoxifen in the treatment of metastatic breast cancer, according to findings presented here at the Fourth European Breast Cancer Conference.

These findings do not necessarily mean that physicians should switch all patients on tamoxifen to exemestane, said principal investigator Robert Paridaens, MD. "We need to let these results settle down," he told Medscape in an interview. "If the patient has an estrogen- or progesterone-responsive disease, and no visceral metastases, then the switch may be feasible. We still need to assess individual patients' tolerability to therapy and develop those treatment regimens accordingly." He did acknowledge, though, that tamoxifen's role may diminish over the next 10 years. Dr. Paridaens is a medical oncologist at the University Hospital Gasthuisberg in Leuven, Belgium.

The open-label phase III trial involved 382 patients from 81 centers in 25 countries. The investigators wanted to know whether exemestane would enable disease-free survival at least three months longer than is seen with tamoxifen, as well as to determine the safety of exemestane.

Of the 190 patients in the exemestane group, 14 (7%) had a complete response to treatment, and 71 (37%) had a partial response. In the tamoxifen group, five patients (3%) had a complete response, and 52 (17%) had a partial response. "Regardless of the site of metastasis, we saw an increased response in those treated with exemestane over those treated with tamoxifen," Dr. Paridaens said in a press briefing.

The average length of progression-free survival was 9.95 months in the exemestane group and 5.72 months in the tamoxifen group. Of all the patients, 284 patients (74%) have either progressed in their breast cancer or have died. The investigators are still assessing the overall survival data and will release their analysis later in 2004.

Dr. Paridaens noted that all aromatase inhibitors, including exemestane, are associated with hot flashes and other menopausal symptoms, as is tamoxifen. He added that aromatase inhibitors are linked to aching sensations in muscles and joints. However, exemestane and other aromatase inhibitors are less likely than tamoxifen to cause blood clots and, unlike tamoxifen, are not linked to endometrial cancer.

Fourth European Breast Cancer Conference: Abstract 241. Presented March 18, 2004.

Reviewed by Gary D. Vogin, MD


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