RecruitingPhase 1Drug trialStudy on the Efficacy and Safety of Neoadjuvant Radiotherapy Combined With Toripalimab, Liposomal Irinotecan, and Capecitabine in the Treatment of pMMR Locally Advanced Rectal Adenocarcinoma With Low Rectal InvolvementThe 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.