Comparison of two different S-1 plus cisplatin dosing schedules as first-line chemotherapy for metastatic and/or recurrent gastric cancer: a multicenter, randomized phase III trial (SOS).

Background: Five-weekly S-1 plus cisplatin (SP5) is one of the standard first-line regimens for advanced gastric cancer (GC), proven in a Japanese phase III study. To enhance the dose intensity of cisplatin, 3-weekly S-1 plus cisplatin (SP3) was developed.
Patients and Methods: This multicenter, randomized, open-label, phase III study evaluated whether SP3 (S-1 80 mg/m(2)/day on days 1-14 and cisplatin 60 mg/m(2) on day 1) was noninferior/superior to SP5 (S-1 80-120 mg/day on days 1-21 and cisplatin 60 mg/m(2) on day 1 or 8) in terms of progression-free survival (PFS). Chemotherapy-naive patients with metastatic, recurrent gastric or gastroesophageal junction adenocarcinoma were randomized 1 : 1 to receive either SP3 or SP5. The trial is registered at ClinicalTrials.gov (NCT00915382).
Results: Between February 2009 and January 2012, 625 patients were randomized at 42 sites in Korea and Japan. With a median follow-up duration of 32.4 months (range, 13.3-48.6 months) in surviving patients, SP3 was not only noninferior but also superior to SP5 in terms of PFS [median 5.5 versus 4.9 months; hazard ratio (HR) = 0.82; 95% confidence interval (CI) 0.68-0.99; P = 0.0418 for superiority). There was no difference in overall survival (OS) between the groups (median 14.1 versus 13.9 months; HR = 0.99; 95% CI 0.81-1.21; P = 0.9068). In patients with measurable disease, the response rates were 60% in the SP3 arm and 50% in the SP5 arm (P = 0.065). Both regimens were generally well tolerated, but grade 3 or higher anemia (19% versus 9%) and neutropenia (39% versus 9%) were more frequent in SP3.
Conclusions: SP3 is superior to SP5 in terms of PFS. However, since the improvement in PFS was only slight and there was no difference in OS, both SP3 and SP5 can be recommended as first-line treatments for patients with advanced GC.
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