Purpose: To define the maximum-tolerated dose (MTD) of S-1, given daily for 2 weeks followed by a 1-week rest, with a fixed dose of cisplatin on the initial day, and to determine the activity and safety of this regimen at the recommended dose (RD) when used as first line treatment of advanced gastric cancer (AGC).
Patients and methods: Cisplatin was fixed at a dose of 60 mg/m2 on day 1 (D1) and the starting dose of S-1 was 60 mg/m2/day (30 mg/m2 bid) (level I) on D1 to D14, every 3 weeks. The dose of S-1 was increased by 5 mg/m2 bid up to 100 mg/m2/day (level V) unless the MTD was achieved.
Results: Sixty-two eligible patients were enrolled. MTD was set at level V with two of three patients developing grade 3 diarrhea or febrile neutropenia. The RD was determined at level IV (90 mg/m2/day). After the first 20 patients were enrolled in phase II, the protocol was amended; the S-1 dose was reduced to 80 mg/m2/day (N=23) because of poor bone marrow recovery. The objective response was observed in 20 of 42 evaluable patients (48%). SD was achieved in 15 (36%). The median PFS was 5.3 months (95% CI, 4.6-6.0 months) with a median OS of 10.0 months (95% CI, 5.1-14.8 months). Grade 3-4 toxicities included neutropenia (33%), anemia (31%), and anorexia (24%).
Conclusions: The 3-week combination of cisplatin plus S-1 is active against AGC with favorable toxicitiy profiles. The phase II schedule or doses may need further refinements.