The Effects of Neoadjuvant Tislelizumab Combined With Chemotherapy in Locally Advanced MSS Rectal Cancer

Inclusion Criteria: * Age ≥18 years old and ≤70 years old. * Pathologically diagnosed MSS ((confirmed by microsatellite stable detection or next-generation target sequencing) or (confirmed by immunohistochemistry)) colon adenocarcinoma. * The lower edge of the tumor is less than 12cm from the anus as measured by colonoscopy and MRI,or TRUS. * It was confirmed by magnetic resonance imaging (MRI) or intracavitary ultrasound of the rectum as T3-4 or N+, and M0 by enhanced CT. * The ECOG physical status score is 0-1. * Life expectancy is expected to be more than 1 year. * First diagnosis, no previous anti-tumor treatment received, and no chemotherapy contraindications. * Appropriate organ function is defined as follows: Hemoglobin level ≥ 90g/L, Neutrophil count ≥ 1.5×10\^9/L, Platelet count ≥ 75×10\^9/L, Serum total bilirubin ≤ 1.5× the upper limit of normal (UNL), Aspartate aminotransferase (AST) ≤ 2× UNL, Alanine aminotransferase (ALT) ≤ 3× UNL, Serum creatinine ≤ 1.5× UNL. * Informed consent, able to understand the study protocol and willing to participate in the study, and will provide written informed consent. Exclusion Criteria: * Early rectal cancer (T1-2N0M0); The lower margin of the tumor was less than 5cm from the anus and T4. APR(combined abdominal perineal resection) is required; * Multifocal colorectal cancer. * Tumor obstruction or high risk of obstruction, bleeding, and/or perforation requiring emergency surgery or stent placement. * Cannot tolerate chemotherapy or immunotherapy, such as but not limited to bone marrow suppression. * History of malignant tumors, except for basal cell carcinoma, papillary thyroid carcinoma, and various in situ cancers. * Acute exacerbation of important organ diseases (such as but not limited to COPD, coronary heart disease, and renal insufficiency) and/or severe acute infectious diseases (such as but not limited to hepatitis, pneumonia, and myocarditis), ASA score \> 3 points. * Mental disorders, illiteracy, or language communication barriers that prevent the understanding of the study protocol. * Peripheral sensory neuropathy, unable to receive oxaliplatin-based chemotherapy. * Continuous use of glucocorticoids for more than 3 days within 1 month prior to signing the informed consent form, or having comorbidities requiring the use of glucocorticoid therapy. * Unable to undergo enhanced CT examination * Pregnancy or lactation. * Refused to participate in this study. * Other situations in which the researcher deems unsuitable for this study.