Clinical Study on the Safety and Relationship of Sintilimab Combined With Chemotherapy in Neoadjuvant Treatment of Locally Advanced Rectal Adenocarcinoma

Inclusion Criteria:1. Pathologically confirmed rectal adenocarcinoma (non-special type and special type, including mucinous adenocarcinoma, signet ring cell carcinoma, serrated adenocarcinoma, micropapillary carcinoma, medullary carcinoma, cribriform comedo adenocarcinoma); preoperative imaging confirmed that the stage is 1) rectal cancer T3 and (or) N+ resectable rectal cancer patients; 2) for T4 patients, re-evaluation of resectability must be conducted after the completion of neoadjuvant therapy, and radiotherapy may be used in combination depending on the situation. 2. Age ≥ 18 years old, gender is not limited, ECOG score 0-2 points; 3. Physical condition and organ function allow for major abdominal surgery/4. Agree that the researchers use blood, stool and pathological sections for research during the study; 5. Major organ function meets the following requirements (laboratory test values within 7 days before enrollment must meet the following standards) ① Routine blood examination: (no blood transfusion, no use of granulocyte colony stimulating factor, no use of drug correction within 14 days before screening): a) Neutrophil ≥ 1.5×109/L; b) Platelet ≥ 75×109/L; c) Hemoglobin ≥ 90g/L; ② Biochemical examination: (no albumin transfusion within 14 days before screening): a) Serum creatinine ≤ 1.5×upper limit of normal (ULN), or creatinine clearance\> 50 mL/min; b) Serum total bilirubin ≤ 1.5×ULN; c) Aspartate aminotransferase (AST), alanine aminotransferase (ALT) ≤ 2.5 × ULN…