Trial of 3-weekly Versus 5-weekly Schedule of S-1 Plus Cisplatin in Gastric Cancer: SOS

Inclusion Criteria: * Histologically documented metastatic or recurrent gastric adenocarcinoma including adenocarcinoma of the gastro-esophageal junction * Age 18 to 74 years old * Performance status (ECOG scale) 0-2 * No significant problems for oral intake and drug administration * At least one measurable or evaluable disease defined by RECIST * Adequate bone marrow function (ANC ≥ 1,500/uL, Platelet ≥ 100,000/ uL, Hb ≥ 9.0 g/dl) * Adequate renal function: serum creatinine ≤ UNL (if serum creatinine \> UNL, creatinine clearance should be ≥ 60 mL/min) * Adequate hepatic function (Total bilirubin \< 2 x UNL and AST/ALT levels \< 3 x UNL without liver metastasis,total bilirubin \< 3x ULN and AST/ALT levels \< 5 x UNL with liver metastasis) * Prior systemic therapy (for instance, cytotoxic chemotherapy or active/passive immunotherapy) is allowed if at least 6 months has elapsed between completion of adjuvant/neoadjuvant therapy and enrolment into the study) and cisplatin was not used before * Patients should sign a written informed consent before study entry Exclusion Criteria: * Tumor type other than adenocarcinoma * Previously exposed to any fluropymidine within 6 months before the study * Previously exposed to Platinum therapy regardless of its period and/or duration * Microscopic residual disease only after noncurative gastrectomy with R1 resection (resection margin positive) * Second primary malignancy (except in situ carcinoma of the cervix or adequately treated basal cell carcinoma of the skin or prior malignancy treated more than 5 years ago without recurrence) * Prior radiotherapy was administered to target lesions selected for this study, or radiotherapy to the non-target lesions has been completed within 4 weeks before randomization * Presence of CNS metastasis * Major surgery within 4 weeks before initiation of study treatment or lack of complete recovery from the effects of major surgery (patient received curative operation or RFA for metastatic disease) * Serious illness or medical conditions: * Congestive heart failure (NYHA class III or IV) * Unstable angina or myocardial infarction within the past 12 months * Significant arrhythmias requiring medication and conduction abnormality such as over 2nd degree AV block * Uncontrolled hypertension * Hepatic cirrhosis (≥ Child class B) * Interstitial pneumonia * Pulmonary adenomatosis * Psychiatric disorder that may interfere with protocol compliance * Unstable diabetes mellitus * Uncontrolled ascites or pleural effusion * Active infection * Receiving a concomitant treatment interacting with S-1 or cisplatin: * Flucytosine (a fluorinated pyrimidine antifungal agent) * Antivirals such as sorivudine, ramivudine, brivudine or other chemically related agents, warfarin, phenprocoumon, phenytoin, allopurinol * Pregnant or lactating woman * Women of child bearing potential not using a contraceptive method * Sexually active fertile men not using effective birth control during medication of study drug and up to 6 months after completion of study drug if their partners are women of child-bearing potential * Any patients judged by the investigator to be unfit to participate in the study