A Study of Neoadjuvant Chemoradiotherapy With 5-FU/Leucovorin (FL) vs. TS-1/Irinotecan in Patients With Locally Advanced Rectal Cancer

Inclusion Criteria: * Histologically confirmed adenocarcinoma of the rectum * AJCC/UICC pathologic stages of cT3-4 or cN plus * Male or female patients, 18 years of age or older * Be ambulatory and have an Eastern Cooperative Oncology Group (ECOG) performance status 0-1. * No prior chemotherapy, radiotherapy and immunotherapy * Adequate major organ functions as following: Hematopoietic function: ANC (absolute neutrophil count)1,500/mm3, Platelet 100,000/mm3, and Hepatic function: serum bilirubin \< 1.5 x ULN, AST/ALT levels \< 2.5 x ULN, and Renal function: serum creatinine \< 1.5 x ULN or Ccr 50 ml/min by Cockcroft formula * Be willing and able to comply with the protocol for the duration of the study. * Give written informed consent prior to study-specific screening procedures, with the understanding that the patient has the right to withdraw from the study at any time, without prejudice. Exclusion Criteria: * Any histologic feature other than adenocarcinoma or arisen from chronic inflammatory bowel disease * Patients treated with previous surgery, chemotherapy and/or radiotherapy * Uncontrolled or severe cardiovascular disease: New York Heart Association class III or IV heart disease, and Unstable angina or myocardial infarction within the past 6 months, and History of significant ventricular arrhythmia requiring medication with antiarrhythmics or significant conduction system abnormality. * Serious concurrent infection or nonmalignant illness that is uncontrolled or whose control may be jeopardized by complications of study therapy. * Other malignancy within the past 5 years except non-melanomatous skin cancer or carcinoma in situ of the cervix. * Organ allografts requiring immunosuppressive therapy. * Psychiatric disorder or uncontrolled seizure that would preclude compliance. * Pregnant, nursing women or patients with reproductive potential without contraception. * Patients receiving a concomitant treatment with drugs interacting with 5-FU or irinotecan such as flucytosine, phenytoin, or warfarin et al. * Prior unanticipated severe reaction to fluoropyrimidine therapy, or known dihydropyrimidine dehydrogenase (DPD) deficiency. * Known hypersensitivity to any of the components of the study medications. * Received any investigational drug or agent within 4 weeks before beginning treatment with study drug.