This study aims to elucidate the effects of neoadjuvant Tislelizumab combined with chemotherapy in locally advanced MSS rectal cancer.

The standard treatment for locally advanced rectal cancer is neoadjuvant chemoradiotherapy followed by total mesorectal excision (TME). Pelvic chemoradiotherapy for locally advanced rectal cancer reduces the risk of disease recurrence in the pelvis to less than 10% and has been standard care in North America since 1990.However, it is associated with short-term and long-term toxic effects that can adversely affect quality of life and physical function.

Immunogenic cell death will be enhanced by oxaliplatin-induced immunogenicity and combined with anti-programmed cell death 1 (PD-1) monoclonal antibodies for neoadjuvant therapy. The study will conduct 2 or 4 cycles of Tislelizumab with Oxaliplatin and Capecitabine, followed by TME surgery. This study's primary endpoint is the proportion of pCR in the pathological specimens of surgically resected tumors.

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.

We will share the research proposal after registration; Primary study endpoint data were shared 15 days after surgery; All data will be shared 3 years after enrollment

We will share the research proposal after registration; Primary study endpoint data were shared 15 days after surgery; All data will be shared 3 years after enrollment

Clinician or researcher