Exploratory Clinical Study of Neoadjuvant Immunotherapy Combined With Chemotherapy in Malignant Melanoma of Nasal and Paranasal Mucosa

Inclusion Criteria: * Histopathologically confirmed diagnosis of malignant melanoma of the nasal cavity and paranasal sinuses. * T stage of T3 or T4a. * Age ≥18 years. * No distant metastasis. * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2, with general condition tolerating chemotherapy and general anesthesia for surgery. * Locally resectable with curative intent, and able to undergo contrast-enhanced CT or contrast-enhanced MRI examinations. * Adequate organ function: Hematology: white blood cells ≥3.0 × 10\^9/L; absolute neutrophil count ≥1.5 × 10\^9/L; hemoglobin ≥80 g/L; platelets ≥100 × 10\^9/L. Hepatic function: total bilirubin ≤1.5 × upper limit of normal (ULN); AST and ALT ≤3 × ULN. Coagulation: international normalized ratio (INR) or prothrombin time (PT) or activated partial thromboplastin time (aPTT) ≤1.5 × ULN. Renal function: serum creatinine ≤1.5 × ULN. * Patients with recurrence after prior curative surgery are allowed; for recurrent patients, chemotherapy and immune therapy must have been discontinued for more than 6 months. Exclusion Criteria: * Patients who refuse to sign the informed consent form. * Patients with uncontrolled comorbidities that, in the investigator's judgment, would interfere with treatment. * Patients currently suffering from another malignant tumor or with synchronous multiple primary tumors that require treatment. * Patients with surgical contraindications, such as severe cardiopulmonary disease or coagulation disorders. * Patients with autoimmune diseases. * Patients currently using immunosuppressants, or receiving systemic glucocorticoids for immunosuppressive purposes (dose \>10 mg/day prednisone or equivalent), and who continue to use them within 2 weeks prior to first dosing. * Prior treatment with PD-1 monoclonal antibodies or PD-L1 monoclonal antibodies; or a history of severe allergic reactions to other monoclonal antibodies. * Receipt of a live vaccine within 6 weeks prior to first dosing, or the possibility of receiving a live vaccine during the study. * Any condition that may compromise protocol adherence or safety during the study. * Uncontrolled active infection. * Pregnant or breastfeeding women. * Any other condition deemed unsuitable for enrollment.