Neoadjuvant Chemotherapy, Anti-PD-1 Antibody and Sitagliptin for Locally Advanced pMMR CRC

Inclusion Criteria: * Pathologically diagnosed colorectal adenocarcinoma * Age ≥18 years old and ≤75 years old * MRI/CT stage T3-4aNany and TanyN1-2, without distant metastasis * Life expectancy of 1 year The above * Informed consent, no contraindications to chemotherapy exist * pMMR diagnosed by IHC Exclusion Criteria: * Refused to participate in this study * Multifocal colorectal cancer * Past history of malignant tumors, except for basal cell carcinoma/papillary thyroid carcinoma/various types of carcinoma in situ * Unable to receive chemotherapy , such as but not limited to bone marrow suppression, etc * Major organ diseases (such as but not limited to COPD, coronary heart disease and renal insufficiency, etc.) acute attack and or severe acute infectious diseases (such as but not limited to hepatitis, pneumonia and myocarditis, etc.), * ASA score\> 3 * Mental disorder or illiteracy or language and communication barriers cannot understand the research plan * Colorectal tumor has obstruction or high risk of obstruction and or there is bleeding and/or perforation * Peripheral sensory nerve disorder, unable to receive oxaliplatin chemotherapy * Lateral pelvic lymph node metastasis (mainly supplied by internal iliac artery) * Pregnancy or breastfeeding * Unable to accept MRI examination * Consecutive use of glucocorticoids for more than 3 days within 1 month before signing the consent form * Diabetes or impaired glucose tolerance who may require drug intervention * Other scenarios deemed inappropriate by the investigators