Advanced breast cancer more responsive to letrozole than anastrozole

As a second-line therapy for advanced breast cancer, letrozole is associated with a higher response rate than anastrozole, new research indicates. Still, both agents seem to provide comparable clinical benefits.

“This study was the first to directly compare the clinical activity of letrozole and anastrozole, as second-line therapy in postmenopausal women with advanced breast cancer after failure on tamoxifen,” lead author Dr. C. Rose, from Lund University Hospital in Sweden, and colleagues note. The new findings are in agreement with in vitro data that letrozole (Femara) is a much stronger inhibitor of aromatase activity than anastrozole (Arimidex), the researchers state. In a study reported in the November issue of the European Journal of Cancer, Dr. Rose’s team assessed the outcomes of 713 postmenopausal women with advanced breast cancer who were randomized to receive letrozole or anastrozole. All of the patients had previously experienced disease progression during or soon after treatment with an anti-estrogen.Forty-eight percent of patients had tumors that were positive for estrogen receptors, progesterone receptors, or both. In the remaining patients, the receptor status was unknown. Letrozole was associated with an overall response rate of 19.1%, significantly higher than the rate seen with anastrozole, at 12.3% (p = 0.013), the investigators point out.Despite the response difference, both treatments were comparable in terms of time to disease progression, the primary efficacy endpoint. The median time to progression with each therapy was 5.7 months, the authors state.In addition, median overall survival was not significantly different between the groups–around 21 months for each. Other clinical outcomes that were similar for the groups included rate and duration of clinical benefit and duration of response. Moreover, both drugs were well tolerated and had similar safety profiles.These results “indicate that advanced breast cancer is more responsive to letrozole than to anastrozole as second-line endocrine therapy,” the researchers conclude.(Source: Eur J Cancer 2003;39:2318-2327: Reuters Health: November 11, 2003: Oncolink)