CD274 and head and neck squamous cell carcinoma: Other data demonstrated that the cytokine-like factor transmembrane protein CMTM6, a direct regulator of the PD-1/PD-L1 axis through the stabilization of PD-L1 protein, has been recently involved in the upregulation of β-catenin activation and in the maintenance of a stemness phenotype in head and neck squamous cell carcinoma.