Evaluation of oral S-1 as a first-line chemotherapy for metastatic HER2-negative breast cancer: An analysis of two randomized phase III studies (SELECT BC-CONFIRM and SELECT BC).

1083 Background: Anthracycline regimens and taxane have been first line chemotherapeutic options for HER2 negative metastatic breast cancer. In a previous phase III trial (SELECT BC), non-inferiority of S-1 was demonstrated in terms of overall survival (OS). The SELECT BC-CONFIRM study was designed to confirm the results of the SELECT BC study and to combine the two randomized studies. Methods: Patients (n = 618) in the first trial were randomly assigned (1:1) to the S-1 group or the taxane group. Patients (n = 230) in the second trial (SELECT BC-CONFIRM) were randomly assigned to the anthracycline group or the S-1 group. Treatment continued until tumor progression, unacceptable toxic effects, or completion of six courses in the standard regimen group and four courses in the S-1 group. The primary endpoint was OS and secondary endpoints were progression-free survival (PFS), time to treatment failure, adverse events, HRQOL and cost-effectiveness. A pooled analysis of the two studies was predefined to confirm the results of the SELECT BC study. Results: 1. The HR for the anthracycline group was 1.09 [95%CI 0.80-1.48] in SELECT BC-CONFIRM, and the estimated predictive posterior probability that the HR does not exceed the threshold 1.333 was 90.27%. 2. Median OS was 32.7 months (S-1 group) and 36.3 months (standard treatment group). S-1 was not inferior to standard treatment in terms of OS (p non-inferiority = 0.0062). Median PFS was 11.2 months (S-1 group) and 11.2 months (standard treatment group). 3. Treatment was discontinued due to adverse events (i.e., neutropenia, febrile neutropenia, fatigue and edema) in 5.7% in the S-1 group and 6.6% in the standard treatment group 4. The EORTC QLQ-C30 questionnaire (global health status) revealed that there was no difference between the S-1 and anthracycline groups (p = 0.257), but there was a significant difference between the S-1 and taxane groups (p = 0.0039). Conclusions: S-1 is not inferior to taxane or anthracycline with respect to OS as a first-line treatment for MBC. S-1 should be considered a new option as a first-line chemotherapy for HER2-negative metastatic breast cancer patients. Clinical trial information: UMIN000005449.