Radiotherapy With Neoadjuvant Chemotherapy and Immunotherapy in Rectal Cancer

Inclusion Criteria: 1. Patients who personally provided written consent for participation in the study 2. Treatment-naive patients with rectal cancer, in whom the inferior margin of the tumor is at a distance of 10 cm or less from the AV before CRT 3. Histologically confirmed adenocarcinoma of rectum (non-metastatic, \>T2N0 or low T2N0 rectal cancer) not eligible for up-front organ preservation surgery as deemed by multidisciplinary evaluation 4. Patients with the ECOG performance status of 0 or 1 at the time of enrollment 5. Women of childbearing potential who consent to practicing contraception during the period from giving informed consent to at least 23 weeks after the last dose of therapy 6. Male patients who consent to practicing contraception during the period from giving informed consent to at least 31 weeks after the last dose of the study drug 7. Patients must have acceptable organ and marrow function as defined below: Absolute neutrophil count (ANC) \>1,500/uL Hg \> 8.0 g/dL; if blood transfusion is performed for achieving adequate hemoglobin level, the level should stay above goal for at least 1 week after transfusion Platelets \>100,000/uL Total bilirubin \<1.5X normal institutional limits aspartate aminotransferase (AST) (SGOT) / alanine aminotransferase (ALT)(SGPT) \< 3X upper limit of normal Creatinine \<1.5X upper limit of normal or creatinine clearance (CrCL)\>50 by Cockcroft-Gault Exclusion Criteria: 1. Patients with recurrent rectal cancer or a history of pelvic radiation 2. Patients with a history of inflammatory bowel disease 3. Patients with a history of pneumonitis or interstitial lung disease 4. Patients with concurrent autoimmune disease or a history of chronic or recurrent autoimmune disease 5. Patients requiring treatment with systemic corticosteroids or immunosuppressants or who have received these treatments within 14 days before enrollment in the study 6. Patients with a history of thyroid dysfunction 7. Patients with a history or finding of cardiovascular risk 8. Patients who are positive for any of the following: HIV1 antibody, HIV2 antibody, HTLV1 antibody 9. Patients who are pregnant or lactating or who may be pregnant 10. Patients with significant unstable mental diseases or other medical diseases that may interfere with the safety of the subjects, obtaining informed consent, or compliance with the procedures for the clinical study