Study of TS-1 or TS-1 + PSK for Gastric Cancer Patients

Inclusion Criteria: * Patient who is pathologically confirmed as gastric cancer * Patient who has received surgery with D2 or more lymph node dissection and whose final curability of surgical resection is grade A or B * Patient whose final stage is II (except for T1), IIIA, or IIIB * Patient without liver, peritoneal and distant metastasis, and who is negative in peritoneal cytological diagnosis * Patient whose age at the registration is ranging between 20 and 80 years old * Patient who has not received any preoperative therapy including radiotherapy, chemotherapy and immunotherapy * Patient who has received surgery for gastric cancer within six weeks before the registration, and is judged to be capable of oral administration * Patient who has no serious concurrent complications, and satisfies the following criteria * White blood cell count: \> LLN or \> 4,000 /mm3 * Platelet count: \> 100,000 /mm3 * Serum total bilirubin: \< 1.5 mg/dL * Serum AST (GOT), ALT (GPT): \< 2.5 \* ULN * Serum creatinine: \< ULN * Patient who has received an explanation of this study by assent documents, and has given written informed consent to participate in this study Exclusion Criteria: * Patient with metachronous or synchronous multicancer * Patient who contraindicates to TS-1 * Patient who requires continuous use of flucytosine, phenytoin or warfarin potassium * Patient who has experienced serious drug allergy over grade 3 in the past * Patient with serious complications including paralysis of intestine, ileus, interstitial pneumonitis, fibroid lung, uncontrollable diabetes mellitus, heart insufficiency, renal insufficiency or hepatic insufficiency * Patient with diarrhea (watery stool) * Patient who is pregnant or in lactation, or wish to become pregnant during this study * Male patient who intends to make someone pregnant during this study * Patient with HIV positive * Patient who is judged to be inappropriate as subject to this study by the principal investigator or the doctors in charge