Adjuvant Capecitabine Versus Observation Alone in Curatively Resected Stage IB Gastric Cancer((KCSG ST14-05): CATALYSIS

Inclusion Criteria: * Curatively resected gastric or gastroesophageal junction adenocarcinoma * Pathologic stage IB (by AJCC 6th edition) with at least one additional risk factor for recurrence (additional risk factors for recurrence include age \>65 years, male gender, presence of lymphovascular invasion, presence of perineural invasion). * Age: 18 -74years * ECOG performance status: 0-2 * Adequate bone marrow function (ANC \>1,500/uL, Platelets 100,000/uL, and Hb \> 8.0 g/dL) * Adequate renal function (serum creatinine \< 1.5 mg/dL) * Adequate hepatic function (bilirubin \< 1.5 mg/dL, ALT and AST \< 3 times upper limit of normal) * Written informed consent Exclusion Criteria: * Pregnant or lactating women. * Women of childbearing potential with either a positive pregnancy test at baseline. Postmenopausal women must have been amenorrheic for at least 12 months to be considered of non-child bearing potential. * Sexually active males and females (of childbearing potential) unwilling to practice contraception during the study medication and until 3 months after discontinuation of the study medication. * Any evidence of metastatic disease (including presence of tumor cells in the ascites). * Previous chemotherapy or radiotherapy for the currently treated gastric cancer. * No recovery from serious complications of gastrectomy. * History of another malignancy within the last five years except cured basal cell carcinoma of skin and cured carcinoma in-situ of uterine cervix. * History of uncontrolled seizures, central nervous system disorders or psychiatric disability judged by the investigator to be clinically significant precluding informed consent or interfering with compliance for oral drug intake. * Clinically significant (i.e. active) cardiac disease: e.g. unstable angina, symptomatic coronary artery disease, New York Heart Association (NYHA) grade II or greater congestive heart failure or serious cardiac arrhythmia requiring medication or myocardial infarction within the last 6 months. * Lack of physical integrity of the upper gastrointestinal tract or those who have malabsorption syndrome likely to influence absorption of capecitabine, or inability to take oral medication. * Serious uncontrolled intercurrent infections or other serious uncontrolled concomitant disease. * Organ allografts requiring immunosuppressive therapy. * Received any investigational drug or agent/procedure, i.e. participation in another trial within 4 weeks before randomization. * Requirement for concurrent use of the antiviral agent sorivudine (antiviral) or chemically related analogues, such as brivudine. * Positive serologic test for HIV