CD274 and head and neck squamous cell carcinoma: The presence of PD‐L1 on the surface of EVs has been recently described not only for various solid tumors, such as breast cancer [132], metastatic melanoma [133], glioblastoma [134], head and neck squamous cell carcinoma [135], and gastric [136] and pancreatic cancer [137], but also for chronic lymphocytic leukemia [138].