This multicenter, randomized, open-label, blinded-endpoint Phase II trial assesses the efficacy and safety of tolecizumab (PCSK9 inhibitor) plus sintilimab/CapeOX chemoimmunotherapy as neoadjuvant treatment for pMMR/MSS locally advanced colon adenocarcinoma (cT3c+). 106 patients are 1:1 randomized to the combination or chemoimmunotherapy alone, with pCR as the primary endpoint.

This is a multicenter, randomized, open-label, blinded-endpoint Phase II clinical trial designed to evaluate the efficacy and safety of tolecizumab (a PCSK9 inhibitor) combined with chemoimmunotherapy (sintilimab plus CapeOX regimen) as neoadjuvant treatment for patients with pMMR/MSS locally advanced colon adenocarcinoma (cT3c stage or above). A total of 106 eligible patients will be randomized 1:1 into two arms: Arm A (tolecizumab + sintilimab + CapeOX) and Arm B (sintilimab + CapeOX), both receiving 4 cycles of neoadjuvant therapy. The primary endpoint is the pathological complete response rate (pCR) after treatment; secondary endpoints include major pathological response rate (MPR), objective response rate (ORR), R0 resection rate, progression-free survival (PFS), overall survival (OS), and the incidence of adverse events (AEs) graded by NCI-CTCAE V5.0. A virtual historical control (single-agent CapeOX neoadjuvant chemotherapy) is set only for sample size calculation. The study will conduct safety follow-up for up to 90 days after the last administration and survival follow-up every 3 months for a total of 3 years, and also collect biological samples for exploratory biomarker analysis to explore the predictive factors of treatment efficacy. All study drugs and related examinations are provided free of charge for participants, and a Data and Safety Monitoring Board (DSMB) is established to monitor the study process and ensure participant safety.

Inclusion Criteria:

• Signed the written informed consent form and voluntarily participate in the study.

Pathohistologically confirmed colon adenocarcinoma with cT3c stage or above. Aged 18 to 80 years, regardless of gender. The lower edge of the tumor is more than 10 cm from the anus. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Sufficient bone marrow, liver, kidney and coagulation functions assessed by laboratory tests (in accordance with the local laboratory reference range).

No previous anti-tumor treatment for the current colon cancer (including radiotherapy, chemotherapy, surgery, etc.).

No pregnancy or lactation for female patients; male patients agree to take effective contraceptive measures during the study.

Exclusion Criteria:

• Previous anti-tumor treatment for the current colon cancer. Previous use of PCSK9 inhibitors or PD-1/PD-L1 inhibitors. Active autoimmune diseases or a history of autoimmune diseases. Receiving immunosuppressant or systemic glucocorticoid therapy (except for local low-dose glucocorticoid use).

Active infection requiring systemic anti-infective treatment. Severe cardiovascular diseases (e.g., severe hypertension, myocardial infarction, heart failure, etc.).

Complicated primary tumor (e.g., tumor perforation, intestinal obstruction without relief after intervention).

Pregnant or lactating women. Other conditions that the investigator deems unfit for participation in the study (e.g., poor compliance, severe organ dysfunction, etc.).