Evaluation of the optimal dosage of S-1 in adjuvant SOX chemotherapy for gastric cancer

Abstract

Gastric cancer (GC) is the second leading cause of cancer‑related mortality worldwide. The usual treatment of GC consists of surgery with additional adjuvant chemotherapy. In the present study, the feasibility and safety of adjuvant S‑1 plus oxaliplatin (SOX) chemotherapy for patients with GC and the optimal dosage of S‑1 were determined. Eligible patients were randomly assigned to either arm A (30 cases) receiving 70 mg/m2S‑1 (in two seperate half doses) daily or arm B (30 cases) receiving 80 mg/m2S‑1 (in two seperate half doses) daily. The S-1 was administered twice daily for 14 days followed by a 7‑day rest period for the third week. A total of 130 mg/m2oxaliplatin was administered on day 1 every 3 weeks for each arm. The cumulative rates of the relative total administration dose of S‑1 at 100% in the 6th treatment course was 71.4% [95% confidence interval (CI), 56.5‑90.3%] in arm A, which was significantly higher than 21.4% (95% CI, 10.5‑43.6%) in arm B (P=0.001). The most common grade 3/4 toxicities were neutropenia (19.6%), thrombocytopenia (19.6%) and vomiting (16.1%). Grade 3/4 thrombocytopenia was observed in 7.1% of patients in arm A and in 32.1% of patients in arm B (P=0.019). With regard to the adverse events induced by S‑1 administration, the incidence of diarrhea (3.6 vs. 42.9%; P<0.001) was significantly higher in arm B than in arm A, as anticipated. Collectively, adjuvant SOX therapy for GC is feasible and safe, and when combined with 130 mg/m2oxaliplatin, 70 mg/m2/day S‑1 appears to the optimal dose.