Preoperative (Chemo)Radiotherapy for Locally Recurrent Rectal Cancer

Inclusion Criteria: * Age between 18 and 75 years * ECOG performance status of 0-1 * Histologically, cytologically, or MRI/contrast-enhanced CT confirmed pelvic recurrence. At least one measurable pelvic lesion according to RECIST 1.1 * No distant metastases outside the pelvis * (Potentially) resectable lesion * No history of radiotherapy within the 6 months prior to enrollment * No prior chemotherapy; or received postoperative adjuvant therapy but not systemic chemotherapy for metastatic lesions * Investigator-assessed life expectancy of at least 24 weeks * Adequate organ function (bone marrow, liver, kidney, and coagulation function) demonstrated within 7 days prior to the first dose, without the use of blood products or hematopoietic growth factors * Not pregnant or breastfeeding. Effective contraception must be used during the study and for 6 months after the last dose * Fully informed and willing to provide written informed consent to participate in the trial Exclusion Criteria: * Severe electrolyte abnormalities * Active coronary artery disease, severe/unstable angina, newly diagnosed angina, or myocardial infarction within 12 months prior to study participation Thromboembolic events such as cerebrovascular accidents (including transient ischemic attacks), pulmonary embolism, or deep vein thrombosis within the past 6 months * New York Heart Association (NYHA) class II or higher congestive heart failure * Human immunodeficiency virus (HIV) infection or known acquired immunodeficiency syndrome (AIDS); untreated active hepatitis (hepatitis B defined as HBV-DNA ≥ 500 IU/ml, or hepatitis C defined as HCV-RNA above the detection limit of the assay) or co-infection with hepatitis B and C * Active inflammatory bowel disease or other colorectal diseases causing chronic diarrhea * Any active, known, or suspected autoimmune disease. Stable conditions not required systemic immunosuppressive therapy are allowed, such as type I diabetes, hypothyroidism requiring only hormone replacement therapy, and skin conditions (e.g., vitiligo, psoriasis, and alopecia) not requiring systemic treatment * Interstitial lung disease, non-infectious pneumonia, or uncontrolled systemic diseases (e.g., diabetes, hypertension, pulmonary fibrosis, or acute pneumonia) * Known or suspected history of allergy to any study-related medications * Clinically detectable second primary malignancy or history of another malignancy within the past 5 years * Pregnant or breastfeeding women, or women with a positive pregnancy test before the first dose, or female participants and their partners unwilling to use strict contraception during the study * Any clinical or laboratory abnormalities or compliance issues that the investigator deems unsuitable for study participation * Severe psychiatric disorders