Disease-free survival was greater with letrozole than tamoxifen in postmenopausal women with early breast cancer.

M e t h o d s Design: Randomized controlled trial (Breast International Group [BIG] 1-98 study). Allocation: Concealed.* Blinding: Blinded {patients, clinicians, outcome assessors, data analysts, and data safety and monitoring committee}†.* Follow-up period: Median 26 months. Setting: Several hundred centers worldwide. Patients: 8028 postmenopausal women 38 to 90 years of age (median age 61 y) with invasive breast cancer positive for estrogen and/or progesterone receptors; primary surgery resulting in clear margins; and adequate hematologic, renal, and hepatic function. Exclusion criteria included evidence of metastatic disease and other cancer in the previous 5 years. Intervention: Letrozole, 2.5 mg daily (n = 4015), or tamoxifen, 20 mg daily (n = 4013), for 2 or 5 years. (Patients allocated to 2-y treatment received the alternate drug for the next 3 y but were censored 30 d after switching for this analysis). Outcomes: Disease-free survival (ended by any recurrence, new cancer in the contralateral breast or elsewhere in the body, or death), systemic disease-free survival (as above but excluding breast events), overall survival, and adverse events. Patient follow-up: 99.8% (intention-to-treat analysis).