BIG 1–98: A randomized double-blind phase III study comparing letrozole and tamoxifen given in sequence vs. alone as adjuvant endocrine therapy for postmenopausal women with receptor-positive breast cancer

LBA528 Background: The Primary Core Analysis (PCA) of BIG 1–98 comparing letrozole (L) to tamoxifen (T) as initial adjuvant endocrine therapy showed that L significantly prolonged disease-free survival (DFS), particularly reducing the risk of relapse in distant sites, compared with T for postmenopausal women with endocrine-responsive breast cancer (BC). The aim of the Second Primary Analysis (SPA) is to compare L and T given in sequence vs. alone. On Mar 15, ‘06, the Data Safety Monitoring Committee (DSMC) will review the results of the 2nd interim analysis of the SPA. We will present safety and efficacy data from this analysis if the DSMC recommends release of the results. Methods: 8028 women were randomized upfront to Tx5 years (yrs) (A), Lx5 (B), Tx2→Lx3 (C), or Lx2→Tx3 (D); 1835 to the 2-arm option of the study (arm A vs. B; Mar ’98 - Mar ‘00) and 6193 to the 4-arm option (arm A vs. B vs. C vs. D; Apr ’99 - May ‘03). The primary endpoint was DFS (time from randomization to first occurrence of invasive...