5-year follow-up results of a JCOG1104 (OPAS-1) phase III non-inferiority trial to compare 4 courses and 8 courses of S-1 adjuvant chemotherapy for pathological stage II gastric cancer

Abstract

Background: Postoperative adjuvant chemotherapy with S-1 for 1 year (corresponding to eight courses) is the standard treatment for pathological stage II gastric cancer. The phase III trial (JCOG1104) investigating the non-inferiority of four courses of S-1 to eight courses was terminated due to futility at the first interim analysis. To confirm the primary results, we reported the results after a 5-years follow-up in JCOG1104.

Methods: Patients histologically diagnosed with stage II gastric cancer after radical gastrectomy were randomly assigned to receive S-1 for eight or four courses. In detail, 80 mg/m²/day S-1 was administered for 4 weeks followed by a 2-week rest as a single course.

Results: Between February 16, 2012, and March 19, 2017, 590 patients were enrolled and randomly assigned to 8-course (295 patients) and 4-course (295 patients) regimens. After a 5-years follow-up, the relapse-free survival at 3 years was 92.2% for the 8-course arm and 90.1% for the 4-course arm, and that at 5 years was 87.7% for the 8-course arm and 85.6% for the 4-course arm (hazard ratio 1.265, 95% CI 0.846-1.892). The overall survival at 3 years was 94.9% for the 8-course arm, 93.2% for the 4-course arm, and that at 5 years was 89.7% for the 8-course arm, and 88.6% for the 4-course arm (HR 1.121, 95% CI 0.719-1.749).

Conclusions: The survival of the four-course arm was slightly but consistently inferior to that of the eight-course arm. Eight-course S-1 should thus remain the standard adjuvant chemotherapy for pathological stage II gastric cancer.

Keywords: 4 courses; 8 courses; Adjuvant chemotherapy; Duration; Gastric cancer; Non-inferiority; Phase III; S-1; Stage II.