This study is a prospective, single-arm, phase II clinical trial involving patients with advanced HNSCC receiving immunotherapy plus platinum-based dual-drug chemotherapy. It aims to evaluate the myeloprotective efficacy of administering trilaciclib prior to immunotherapy and platinum-based chemotherapy. The objective is to reduce the incidence of chemotherapy-induced myelosuppression (CIM) through pre-chemotherapy myeloprotection, thereby enabling patients to receive chemotherapy on schedule and at full dose. This approach is intended to ensure the efficacy of the chemotherapy regimen and ultimately achieve survival benefits for the patients.