Phase III Study of Letrozole Versus Tamoxifen as First-Line Therapy of Advanced Breast Cancer in Postmenopausal Women: Analysis of Survival and Update of Efficacy From the International Letrozole Breast Cancer Group

Purpose: To analyze overall survival (OS) and update efficacy data for letrozole versus tamoxifen as first-line therapy in postmenopausal women with locally advanced or metastatic breast cancer. Patients and Methods: This multicenter phase III trial randomly assigned 916 patients with hormone receptor–positive or unknown tumors letrozole 2.5 mg (n = 458) or tamoxifen 20 mg (n = 458) daily until disease progression. Optional cross-over was permitted at the treating physician’s discretion. This report updates efficacy at a median follow-up of 32 months. Results: The superiority of letrozole to tamoxifen was confirmed for time to progression (median, 9.4 v 6.0 months, respectively; P < .0001), time to treatment failure (median, 9 v 5.7 months, respectively; P < .0001), overall objective response rate (32% v 21%, respectively; P = .0002), and overall clinical benefit. Median OS was slightly prolonged for the randomized letrozole arm (34 v 30 months, respectively). Although this difference in OS is not significant, survival was improved in the randomized letrozole arm over the first 2 years of the study. Approximately one half of the patients in each arm crossed over. Total duration of endocrine therapy (“time to chemotherapy”) was significantly longer (P = .005) for patients initially on letrozole (median, 16 months) than for patients initially on tamoxifen (median, 9 months). Time to worsening of Karnofsky performance score was significantly delayed with letrozole compared with tamoxifen (P = .001). Conclusion: This study documents the superiority of letrozole over tamoxifen in first-line endocrine therapy in postmenopausal women with advanced breast cancer.