The goal of this clinical trial is to evaluating the efficacy and safety of radiotherapy combined with Tislelizumab, Liposomal Irinotecan, and Capecitabine in patients with locally advanced mid-lower rectal cancer with pMMR.. Patients would be included as:1. Aged between 18-75 years, with no gender restrictions; 2. Biopsy pathology confirmed as pMMR type locally advanced mid-lower rectal adenocarcinoma (tumor lower margin ≤ 10 cm from the anal verge); 3.With the following high-risk factors: T3N+/T4/N2/EMVI+/MRF+/lateral lymph node metastasis/inability to preserve anal function during surgery; 4. No distant metastasis observed in routine chest and abdominal CT scans.

Here is the updated format for the **Eligibility Criteria** with bullet points for each item:

Inclusion Criteria:

• Age: 18-75 years, no gender restriction
• ECOG score 0-1
• Biopsy-confirmed pMMR (proficient mismatch repair) localized advanced low rectal adenocarcinoma (tumor's lower edge ≤ 10 cm from the anus)
• Presence of the following high-risk factors: T3N+/T4/N2/EMVI+/MRF+/lateral lymph node metastasis/inability to undergo sphincter-preserving surgery
• Routine chest and abdominal CT scans showing no distant metastasis
• Bone marrow function: Neutrophil count (ANC) ≥ 1.5 × 10^9/L, platelet count (PLT) ≥ 100 × 10^9/L, hemoglobin (Hb) ≥ 70 g/L
• Liver function: ALT, AST ≤ 2.5 × ULN (upper limit of normal); total bilirubin ≤ 1.5 × ULN; serum albumin ≥ 3 g/dL
• Kidney function: Serum creatinine (Cr) ≤ 1.5 × ULN or creatinine clearance ≥ 60 ml/min (calculated using the Cockcroft-Gault formula)
• For females and patients with reproductive potential, a negative pregnancy test must be done within 72 hours before starting the treatment, and the patient must agree to avoid pregnancy during the study treatment and for 6 months after the treatment. For males with reproductive potential partners, the patient must agree to use adequate medically approved contraception during and for 90 days after the final study treatment
• Patients must agree to receive the study's neoadjuvant chemotherapy regimen and sign an informed consent form

Exclusion Criteria:

• Patients with a history of other malignancies within the past 5 years (except for cured and non-recurring cancers such as in situ carcinoma, basal cell carcinoma of the skin, etc.)
• Patients with active, uncontrolled bacterial, viral, or fungal infections requiring systemic treatment, defined by persistent signs/symptoms related to infection, which do not improve despite appropriate antibiotics, antiviral treatments, and/or other therapies
• Patients with uncontrolled systemic diseases, including unstable angina, myocardial infarction, congestive heart failure, severe unstable ventricular arrhythmia, history of severe pericardial disease, or other cardiovascular diseases; uncontrolled hypertension (defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg despite appropriate antihypertensive treatment), or a history of hypertensive crisis, hypertensive encephalopathy; uncontrolled diabetes (fasting blood glucose ≥ 10 mmol/L), etc.
• Patients known to be allergic or intolerant to the treatment drugs or excipients used in this study
• Any clinical indicators showing contraindications to chemotherapy and surgery
• Patients using strong inhibitors or inducers of enzymes such as CYP3A4, CYP2C8, and UGT1A1
• Pregnant or breastfeeding women, and female patients of reproductive potential who refuse to use appropriate contraceptive measures during the study
• Patients who participated in other clinical trials within 4 weeks before enrollment
• Patients whom the investigator deems unsuitable for participation in the study