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Letrozole in the Extended Adjuvant Treatment of Postmenopausal Women with History of Early-Stage Breast Cancer Who Have Completed 5 Years of Adjuvant Tamoxifen

Authors' Affiliation: Division of Oncology Drug Products, Center for Drug Evaluation and Research, Food and Drug Administration, Rockville, Maryland

Requests for reprints: Bhupinder S. Mann, Food and Drug Administration, HFD-150, 5600 Fishers Lane, Rockville, MD 20857. Phone: 301594-5692; E-mail: mannb{at}cder.fda.gov.

Abstract

Purpose: To present the basis of the decision of the Food and Drug Administration to grant accelerated approval for letrozole for extended adjuvant treatment of early-stage breast cancer in postmenopausal women after completion of adjuvant tamoxifen.

Experimental Design: The Food and Drug Administration reviewed the data from the MA17 trial, a single, multinational, randomized, double-blind, and placebo-controlled trial, submitted by the applicant to support the proposed new indication.

Results: MA17 consisted of a core study and Lipid and Bone Mineral Density safety substudies. It enrolled 5,187 patients. In the core study, median treatment duration was 24 months and median follow-up duration was 27.4 months. Using a conventional definition of disease-free survival, 122 events on letrozole and 193 events on placebo were observed (hazard ratio, 0.62; 95% confidence interval, 0.49-0.78; P = 0.00003). Distant disease-free survival also improved with letrozole, 55 versus 92 events (hazard ratio, 0.61; 95% confidence interval, 0.44-0.84; P = 0.003). No statistically significant improvement in overall survival was observed. Hot flushes, arthralgia/arthritis, myalgia, and new diagnosis of osteoporosis were more common on letrozole. Frequency of fractures and cardiovascular ischemic events was not significantly different. A statistically significant mean decrease in bone mineral density in the hip occurred at 24 months on letrozole.

Conclusions: Letrozole administration led to a statistically significant prolongation in disease-free survival. Fractures and cardiovascular events were similar to placebo; however, new diagnoses of osteoporosis were more frequent. Short duration of treatment and follow-up precluded assessment of long-term safety and efficacy. Thus, accelerated approval was granted instead of regular approval.