CD137 is a potent costimulatory receptor on activated T cells, which enhances anti-tumor immune response when CD137 levels are upregulated, while its negative feedback mechanism shifts CD137 from T cells to APC expressing CD137 ligand, forming CD137-CD137 ligand complex for degradation, accordingly, leading to immune escape.[61] The results of a study further revealed that PD-L1 is overexpressed in laryngeal squamous cell carcinoma (LSCC) and hypopharyngeal squamous cell carcinoma tissues and is expressed at higher levels in vocal and subglottic compared to supraglottic LSCC tissues. Here, CD274 is linked to neoplasm.