Surufatinib Plus mFOLFIRINOX and PD-1 Inhibitor as the Neoadjuvant Therapy for High-risk or Borderline Resectable Pancreatic Cancer

This study is a single-center, single-arm, phase II study. Preoperative neoadjuvant treatment plan: * Surufatinib: 200 mg orally once daily, continuous dosing, with a 14-day treatment cycle; * Toripalimab: 3 mg/kg per dose, intravenous infusion over 1 hour on day 1, every 14 days per treatment cycle; * Oxaliplatin: 68 mg/m² intravenous infusion over 2 hours on day 1; * Irinotecan: 135 mg/m² intravenous infusion over 30-90+ minutes on day 1; * Calcium folinate: 400 mg/m² intravenous infusion over 2 hours on day 1; * 5-FU: 2400 mg/m² continuous intravenous infusion over 46 hours; repeated every 14 days per treatment cycle. Neoadjuvant treatment will be administered for up to 8 cycles. During treatment, tumor assessments using imaging will be conducted every 8 weeks (±7 days). For patients achieving stable disease, partial response, or complete response, it will be evaluated whether surgery is feasible. Surgery should occur at least 2 weeks after the last neoadjuvant treatment. Postoperative adjuvant treatment plan: * Adjuvant treatment will begin within 4-8 weeks after surgery, with the specific regimen determined by the investigator. * During postoperative adjuvant treatment, tumor assessments using imaging will be conducted every 8 weeks (±7 days) until disease progression (RECIST 1.1) or death (during patient treatment), or until intolerable toxicity occurs. Subsequent treatment after disease progression and survival status will also be recorded.