CTLA4 and head and neck squamous cell carcinoma: Analysis of the TCGA HNSCC dataset revealed that CXCR2, CSF1R and CTLA-4 are significantly expressed in HNSCC samples compared to other tumor types, and we validated the expression of CXCR2 on sorted peripheral blood gMDSC and CSF1R on mMDSC from an independent cohort of patients with advanced pharyngeal SCC.