Envafolimab Combined With Chemotherapy in Neoadjuvant and Conversion Therapy for Head and Neck Squamous Cell Carcinoma

envafolimab: 150 mg once every 1 week for 8 doses subcutaneously on day 1 Chemotherapy: nab-paclitaxel + cisplatin/carboplatin 3 cycles; Albumin paclitaxel 260 mg/m2, cisplatin 75 mg/m2 divided into 3 days, carboplatin AUC 5 applied on the first day.