Serplulimab Plus Decitabine and CAPOX Before Surgery for Locally Advanced Colorectal Cancer

Inclusion Criteria: * Voluntarily signs written informed consent before screening. * Male or female, aged 18 years or older. * Has at least one measurable lesion according to RECIST version 1.1. * ECOG performance status score of 0 to 1. * Histologically or pathologically confirmed colorectal adenocarcinoma with no prior antitumor treatment, staged as cT3/cT4N+M0 locally advanced colorectal cancer according to the AJCC/UICC 8th edition based on contrast-enhanced CT or MRI, with colonoscopy and/or diagnostic laparoscopy if clinically indicated. * Planned to undergo surgery after neoadjuvant therapy according to clinical staging. * Expected survival of more than 3 months. * Adequate major organ function, meeting all of the following criteria: * Hematology: neutrophil count ≥1.5 × 10\^9/L, platelet count ≥100 × 10\^9/L, hemoglobin ≥90 g/L, and white blood cell count ≥3.5 × 10\^9/L, without blood transfusion, granulocyte colony-stimulating factor, or other hematopoietic growth factors within 14 days before screening. * Hepatic function: ALT and AST ≤2.5 × upper limit of normal, and total bilirubin ≤1.5 × upper limit of normal, or ≤3 × upper limit of normal for patients with Gilbert syndrome. * Renal function: serum creatinine ≤1.5 × upper limit of normal or creatinine clearance ≥60 mL/min. * Coagulation function: activated partial thromboplastin time, international normalized ratio, and prothrombin time ≤1.5 × upper limit of normal. Exclusion Criteria: * Prior treatment with any antitumor therapy, including chemotherapy, radiotherapy, hormonal therapy, or molecular targeted therapy. * Prior immunotherapy with anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, anti-CTLA-4 antibody, or any other antibody or drug targeting T-cell co-stimulation or immune checkpoint pathways. * History of another malignancy within 5 years or concurrent malignancy, except cured carcinoma in situ of the cervix, non-melanoma skin cancer, or other malignancy treated with curative intent with no evidence of disease for at least 5 years. * Pre-existing peripheral neuropathy of grade 2 or higher according to NCI-CTCAE version 5.0. * Known active central nervous system metastasis and/or carcinomatous meningitis. * History of severe hypersensitivity reaction to any component of a product or formulation similar to the study PD-1 antibody, or known severe hypersensitivity reaction to other monoclonal antibodies, oxaliplatin, capecitabine, or related compounds, defined as NCI-CTCAE version 5.0 grade 3 or higher. * Known history of hereditary bleeding disorder or coagulation disorder associated with bleeding risk. * Major surgery within 4 weeks before enrollment. * Has not recovered from complications of prior surgery to grade 1 or lower according to CTCAE version 5.0, except alopecia and fatigue. * Requires immunosuppressive medication within 2 weeks before enrollment or during the study, except intranasal, inhaled, topical, or local steroid injections; systemic corticosteroids at physiological doses equivalent to prednisone ≤10 mg/day; or short-term use of steroids for prevention or treatment of non-autoimmune allergic conditions for no more than 7 days. * Active autoimmune disease or history of autoimmune disease with potential recurrence. * Known history of interstitial lung disease or non-infectious pneumonitis. * Known history of active tuberculosis. * History of human immunodeficiency virus infection, other acquired or congenital immunodeficiency disease, organ transplantation, or stem cell transplantation. * Positive hepatitis B surface antigen with HBV DNA ≥10\^4 copies/mL or ≥2000 IU/mL at screening, or active hepatitis C defined as positive HCV antibody with HCV RNA above the lower limit of detection. * Active or uncontrolled infection requiring systemic treatment within 2 weeks before enrollment. * Receipt of a live viral vaccine within 4 weeks before enrollment. * Intestinal obstruction, inflammatory bowel disease, extensive intestinal resection with chronic diarrhea, Crohn's disease, ulcerative colitis, or chronic diarrhea. * Breastfeeding, or planning pregnancy during treatment and within 6 months after completion of treatment. * Unwillingness to use effective contraception during treatment and within 6 months after completion of treatment, including male participants capable of fathering a child, female participants, and their male partners. * Any other condition that, in the investigator's judgment, may affect protocol compliance or assessment of study endpoints and makes the participant unsuitable for this study.