CD274 and head and neck squamous cell carcinoma: Recent evidence suggests that the expression of PD-L1 on the surface of exosomes may be one reason for the low efficacy of anti-PD-L1/PD-1 therapy, including glioblastoma, nonsmall-cell lung cancer, head and neck squamous cell carcinoma, prostate cancer, oral-oesophageal cancer, and colorectal cancer (Yin et al., 2021).