CD274 and head and neck squamous cell carcinoma: Although a meta-analysis of pre-treatment PD-L1 CTC expression in HNSCC did not reveal significant associations with progression-free survival, Strati et al. reported that increased PD-L1 expression on CTCs in locally advanced HNSCC was an independent prognostic marker of decreased overall survival and progression-free survival after radio-chemotherapy62–65.