4028 Background: We conducted a randomized phase II study to compare continuous vs. intermittent S-1 + oxaliplatin (SOX) after induction of 6 cycles of SOX in patients (pts) with metastatic gastric cancer (MGC). Methods: Pts >18 yrs with chemo-naive MGC, normal organ function, ECOG PS 0-2, and measurable or evaluable lesion(s) were initially given an induction treatment of 6 cycles of SOX (S-1 40 mg/m2 bid on D1-14 + oxaliplatin 130 mg/m2 on D1 q 3 wks). Pts with CR/PR or SD were randomized to continue SOX (arm A) until progression/intolerable toxicity or discontinue until progression when SOX was re-administered (arm B). The primary endpoint was overall survival (OS), and secondary endpoints included progression-free survival (PFS), response rate, safety, quality of life, and biomarker correlative studies. Results: From July 2007 to Dec 2010, a total of 250 pts entered into the study. Median age was 53 yrs (range, 24-69); PS 0/1/2=13/219/18; M/F=162/88. Three pts did not receive treatment and 126 (50.4%) discontinued treatment before or at the completion of 6 cycles of SOX due to progression (45.6%), pt refusal (2.8%), or adverse events (2.0%). A total of 121 pts were randomized: 59 (48.8%) to arm A and 62 (51.2%) to arm B. Clinical characteristics were well balanced between arms. SOX continuation resulted in a significant reduction in the risk of progression (median PFS, 10.5 months for arm A vs. 7.2 months for arm B; HR=0.57, 95% CI 0.39-0.84, p=0.005). With a median follow-up of 34.0 months (range, 10.5-53.3 months), there was no significant difference in OS (median OS, 22.6 months for arm A vs. 22.7 months for arm B; HR, 0.79, 95% CI 0.51-1.25, p=0.31). Arm A had higher rates of grade 3/4 fatigue (28.8% vs. 8.1%, p=0.004) and neuropathy (25.4% vs. 8.1%, p=0.014) but other grade 3/4 hematologic (neutropenia, 35.6% vs. 32.3%; thrombocytopenia, 23.7% vs. 21.0%; anemia, 15.3% vs. 6.5%) or non-hematologic toxicity rates were not significantly different. Conclusions: Continuous chemotherapy with SOX after induction therapy improved PFS but not OS. Supported by NCC Grant 1010180 (S-1 and oxaliplatin was provided by JEIL Pharm. Co., Ltd. and sanofi-aventis Korea Co., Ltd., respectively).