Abbreviated R-CHOP in Completely Excised Stage I or II DLBCL

Inclusion Criteria: * Patients who underwent curative resection of primary tumor * Pathologically confirmed CD20 positive diffuse large B-cell lymphoma (DLBCL) after surgical resection * Ann Arbor Stage I or II * No history of chemotherapy * Performance status: ECOG 0-2 * Age: 18 to 70 years old * Complete excision with negative resection margin on pathologic report after surgery * Cardiac ejection fraction ≥ 50% as measured by MUGA or 2D echocardiography without clinically significant abnormalities * Adequate renal function: serum creatinine level below 2 mg/dL (177μmol/L) * Adequate liver functions: Transaminase (AST/ALT) \< 3X upper normal value, Bilirubin \< 2X upper normal value * Adequate hematologic function: hemoglobin ≥ 9 g/dL, absolute neutrophil count (ANC) ≥ 1,500/mm3 and platelet count ≥ 75,000/mm3 * Informed consent Exclusion Criteria: * Patients with a known history of HIV (+) or HCV (+). However, HBV(+) patients are eligible if primary prophylaxis is given * Previous or concurrent cancer that is distinct in primary site or histology from DLBCL, EXCEPT cervical carcinoma in situ, treated basal cell carcinoma, superficial bladder tumors (Ta, Tis \& T1). Any cancer curatively treated \> 3 years prior to entry is permitted * Pregnant or lactating women, women of childbearing potential not employing adequate contraception * Other serious illness or medical conditions 1. Unstable cardiac disease (i.e. congestive heart failure, arrhythmia symptomatic coronary artery disease) despite treatment, myocardial infarction within 6 months prior to study entry 2. History of significant neurological or psychiatric disorders including dementia or seizures 3. Active uncontrolled infection (viral, bacterial or fungal infection) 4. Other serious medical illnesses * Known hypersensitivity to any of the study drugs or their ingredients * Concomitant administration of any other experimental drug under investigation, or concomitant chemotherapy, hormonal therapy, or immunotherapy * Patient with B symptoms or Bulky disease