Long-term health status as measured by EQ-5D among patients with metastatic breast cancer: comparison of first-line oral S-1 and taxane therapies in the randomized phase III SELECT BC trial

Purpose: The goal of chemotherapy for metastatic breast cancer (MBC) is to prolong survival and maintain health-related quality of life. This study aimed to evaluate long-term health status of patients with MBC who participated in the phase III randomized SELECT BC trial. Methods: In the SELECT BC trial, patients were randomly allocated to the S-1 or taxane (paclitaxel or docetaxel) arm. Health status was assessed by EQ-5D at pre-treatment, 3 and 6 months after randomization, and every 6 months thereafter to the extent possible. Least square mean scores were assessed to compare EQ-5D index values between groups. Time to deterioration analysis was also performed by defining the minimally important difference of EQ-5D as 0.05 or 0.1. Results: The number of patients for EQ-5D analysis was 175 and 208 in the taxane and S-1 arms, respectively. Least square mean EQ-5D index values up to 60 months were 0.741 (95 % CI [0.713–0.769]) in the taxane arm and 0.748 [0.722–0.775] in the S-1 arm. The EQ-5D index value during PFS up to 12 months in the S-1 was superior to the corresponding index value in the taxane (0.812 [0.789–0.834] vs. 0.772 [0.751–0.792], P = 0.009). Time to deterioration analysis also revealed that S-1 significantly delayed the deterioration of EQ-5D index value during the period before progression (P = 0.002 and 0.003). Conclusions: Our findings suggest that the EQ-5D index value was higher in patients treated with S-1 during first-line chemotherapy. Considering non-inferiority of S-1 in terms of OS, obtained quality-adjusted life years may be greater in the S-1 arm.