Radical Concurrent Chemoradiotherapy With DDP/5-FU and PD-1 Antibody for Non-metastatic Rectal Squamous Cell Carcinoma

Inclusion Criteria: 1. Voluntarily sign the informed consent; 2. 18-75 years old; 3. Patients with pathologically confirmed rectal squamous cell carcinoma; 4. imaging to rule out distant metastases; 5. Peripheral blood and liver and kidney function before treatment within the following allowable limits (tested within 14 days before the start of treatment) 1. White blood cell (WBC) ≥ 3.0×109/L or neutrophil (ANC) ≥1.5×109/L; 2. Hemoglobin (HGB) ≥80 g/L; 3. Platelets (PLT) ≥ 100×109/L; 4. Hepatic transaminases (AST/ALT) \< 3.0 times the upper limit of the normal range; 5. Total bilirubin (TBIL) \< 1.5 times the upper limit of the normal range; 6. Creatinine (CREAT) \< 1.5 times the upper limit of the normal range. 6. ECOG performance status score of 0-2; 7. No history of other malignant tumors in the past. Exclusion Criteria: 1. Non-treatment-naïve patients who have previously received chemotherapy, radiotherapy or complete surgical resection of rectal squamous cell carcinoma; 2. Distant metastases (M1) confirmed by whole-body CT, MR, or PET-CT (including at least the chest, abdomen, and pelvis); 3. Previous or concurrent presence of other active malignancies (except for malignant tumors that have received curative therapy and have been disease-free for more than 3 years or carcinoma in situ that can be cured by adequate treatment); 4. Major surgery such as laparotomy, thoracotomy, resection of organs by laparoscopic surgery or severe trauma within the past 4 weeks (the surgical incision should be completely healed before randomization); 5. Active coronary artery disease, severe/unstable angina pectoris or newly diagnosed angina pectoris or myocardial infarction within 12 months prior to enrollment in the study; 6. Thrombotic or embolic events such as cerebrovascular accident (including transient ischemic attack), pulmonary embolism, deep vein thrombosis within the past 6 months; 7. New York Heart Association (NYHA) Class II or above congestive heart failure; 8. Prior receipt of any investigational drug; 9. Pregnant or lactating women; 10. Any medical condition that is unstable or would affect patient safety and their compliance with the study; 11. Patients judged by the investigator to be unsuitable to participate in this clinical trial.