Modified SCRT Followed by Tislelizumab Plus CAPOX for Locally Advanced Rectal Cancer

Inclusion Criteria: * Age 18-75 years, any gender. * Pathologically confirmed rectal adenocarcinoma. * Baseline MR stage T3-4/N+. * Distance from anal verge ≤12cm. * No distant metastasis. * Karnofsky Performance Status ≥70. * Adequate organ function, no contraindications to surgery, radiotherapy, or immunotherapy. * Microsatellite/mismatch repair status MSS/pMMR. * No prior chemotherapy or any other anti-tumor treatment before inclusion. * No prior immunotherapy. * Ability to comply with the study protocol during the study period. * Signed written informed consent. Exclusion Criteria: * Pregnant or lactating women. * Pathological diagnosis of signet ring cell carcinoma. * History of other malignancies within the past 5 years, except cured skin cancer and cervical carcinoma in situ. * Uncontrolled epilepsy, central nervous system disorders, or history of psychiatric disorders that, in the opinion of the investigator, may interfere with signing the informed consent form or affect patient compliance with oral medication. * Clinically significant (i.e., active) cardiac disease, such as symptomatic coronary artery disease, New York Heart Association (NYHA) Class II or greater congestive heart failure, or significant arrhythmias requiring drug intervention (see Appendix 12), or history of myocardial infarction within the past 12 months. * Organ transplant recipients requiring immunosuppressive therapy and long-term steroid users. * Patients with autoimmune diseases. * Severe un…