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

Abstract

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 BC recurrence, invasive contralateral BC, second non-breast malignancy, or death from any cause). The SPA is comprised of two pair-wise comparisons: arm A vs. C and B vs. D. Only 4-arm patients (pts) alive and disease-free at 2 yrs after study entry (corresponding to the treatment switch for arms C and D) are included. These analyses will determine if the risk of an event beyond 2 yrs is reduced by switching agents. Additional exploratory analyses based on all events and follow-up (FU) for 4-arm pts will be conducted, including the comparison of arm B vs. C. The final SPA is planned for Feb ‘08, after 662 events. In Jan ‘05, the 1st interim efficacy analysis was presented to the DSMC, after 162 events among 3641 pts (excluding those who had an event within 2 yrs or did not yet have at least 2 yrs of FU). The median SPA FU (from 2 yrs after study entry) was 11.1 months. The 2nd interim efficacy analysis will be presented to the DSMC on Mar 15, ‘06 based on data received as of a Dec 21, ‘05. Results: Conclusions: No significant financial relationships to disclose.