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

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Title:A Single-Arm, Single-Center, Phase II Exploratory Study of Serplulimab Combined with Decitabine plus CAPOX as Neoadjuvant Therapy for Locally Advanced Colorectal Cancer Background:Colorectal cancer is one of the most common gastrointestinal malignancies worldwide. Patients with locally advanced colorectal cancer remain at high risk of recurrence and distant metastasis after surgery. Although perioperative chemotherapy has improved clinical outcomes, the pathological complete response rate remains limited. Immune checkpoint inhibitors have shown remarkable efficacy in dMMR/MSI-H colorectal cancer; however, most pMMR/MSS tumors respond poorly to immunotherapy alone. Decitabine, a DNA methyltransferase inhibitor, may enhance tumor immunogenicity by promoting tumor antigen expression, improving antigen presentation, increasing immune cell infiltration, and reshaping the tumor immune microenvironment. CAPOX chemotherapy may further induce immunogenic cell death and enhance antitumor immune responses. Therefore, the combination of serplulimab, decitabine, and CAPOX may provide a synergistic neoadjuvant treatment strategy for locally advanced colorectal cancer. Objective:This study aims to evaluate the efficacy and safety of serplulimab combined with decitabine plus CAPOX as neoadjuvant therapy for patients with locally advanced colorectal cancer. The primary endpoint is pathological complete response rate. Secondary endpoints include R0 resection rate, tumor downstaging, objective response rate, disease-free survival, and safety outcomes. Methods:This is a prospective, single-center, single-arm, phase II exploratory clinical study. A total of 35 patients with previously untreated locally advanced colorectal adenocarcinoma will be enrolled. Eligible patients are adults aged ≥18 years with histologically or pathologically confirmed cT3/cT4N+M0 colorectal adenocarcinoma according to the AJCC/UICC 8th edition, at least one measurable lesion according to RECIST 1.1, ECOG performance status of 0-1, adequate organ function, and an expected survival of more than 3 months. The study includes a safety lead-in stage and a dose-expansion stage. In the safety lead-in stage, decitabine dose escalation will follow a conventional 3+3 design, with two planned dose levels: 10 mg and 15 mg intravenously on Days 1-2 of each 3-week cycle. Serplulimab will be administered at 300 mg intravenously on Day 1 of each 3-week cycle. CAPOX consists of oxaliplatin 130 mg/m² intravenously on Day 1 and capecitabine 1000 mg/m² orally twice daily on Days 1-14 of each 3-week cycle. The maximum tolerated dose or recommended phase II dose of decitabine will be determined based on dose-limiting toxicity. In the dose-expansion stage, patients will receive serplulimab combined with decitabine and CAPOX for four cycles as neoadjuvant therapy. Patients without distant metastasis and considered suitable for surgery will undergo radical colorectal cancer resection 2-4 weeks after completion of neoadjuvant treatment. Postoperative adjuvant therapy will be determined by the investigator according to pathological findings and clinical practice. Endpoints and Analysis:The primary endpoint is pathological complete response, defined as the absence of residual viable tumor cells in the primary tumor and resected lymph nodes after neoadjuvant therapy. Secondary endpoints include R0 resection rate, tumor downstaging rate, objective response rate assessed by RECIST 1.1, and disease-free survival. Safety assessments include adverse events, serious adverse events, immune-related adverse events, laboratory abnormalities, vital signs, 12-lead ECG, ECOG performance status, thyroid function, and physical examination findings. Adverse events will be graded according to NCI-CTCAE version 5.0. Descriptive statistics will be used for analysis. Continuous variables will be summarized by mean, standard deviation, median, minimum, and maximum. Categorical variables will be summarized by frequency and percentage. Time-to-event outcomes will be analyzed using the Kaplan-Meier method. Expected Significance:This study will explore whether the combination of PD-1 blockade, epigenetic modulation, and CAPOX chemotherapy can improve pathological response while maintaining acceptable safety in locally advanced colorectal cancer. The results may provide preliminary evidence for a new neoadjuvant treatment strategy and support future multicenter clinical studies.

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