Optimal Duration of Oxaliplatin in Adjuvant XELOX for Gastric Cancer Patients (EXODOX)

Inclusion Criteria:

* Histologically or cytologically confirmed gastric or gastroesophageal junction adenocarcinoma patients who underwent curative surgery (D1 beta or D2 resection)
* Pathologically confirmed stage II, III patients (AJCC 8th edition)
* Age 19 years and older
* Eastern Cooperative Oncology Group (ECOG) performance status 0 or 2
* Adequate marrow function (ANC \> 1,500/uL, Platelet \>100,000/uL, Hb \> 8.0 g/dL, patients with chronic anemia who require intermittent blood transfusions can also participate in the study)
* Adequate renal function, with serum creatinine \< 1.5 x upper limit of normal (ULN).
* Adequate hepatic function with serum total bilirubin ≤ 1.5 x ULN, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x ULN
* Written, informed consent to the study

Exclusion Criteria:

* Female patients who are pregnant or breast-feeding
* Positive pregnancy test at baseline (postmenopausal women should be amenorrhea for at least 12 months to be considered non-fertile)
* Sexually active men and women who are not willing to implement contraception during study and until 3 months after discontinuation of study drug
* Evidence of metastasis (including cytologically confirmed malignant ascites)
* Prior systemic chemotherapy or radiation therapy for stomach cancer
* Patients who have not recovered from serious complications of gastrectomy
* History of other malignancies within the last 3 years (excluding adequately treated basal cell carcinoma of the skin, in situ cancer of the cervix, non-metastatic thyroid cancer)
* A history of clinically significant uncontrolled seizures, central nervous system disorders, or mental disorders, which make it impossible to understand the informed consent or interfere with compliance with oral drug intake
* Clinically significant (i.e., active) heart disease: e.g. unstable angina requiring medication, symptomatic coronary artery disease, congestive heart failure with NYHA grade II or higher, severe cardiac arrhythmias or acute coronary syndrome in the past 6 months (including myocardial infarction)
* Lack of integrity or malabsorption syndrome in the upper gastrointestinal tract, which is likely to affect the absorption of study drug
* Serious uncontrolled infection or other serious uncontrolled disease
* History of allograft requiring immunosuppression therapy
* Received any investigational drug or procedure within 4 weeks prior to randomization
* Active viral infection (for hepatitis B carrier, patients can be registered if HBV-DNA titer is less than 20,000 IU/mL, and are allowed to use prophylactic antiviral agents by investigator's choice)
* Active HIV infection
* Patients with peripheral sensory neuropathy with functional impairment