EGFR and head and neck squamous cell carcinoma: Furthermore, stimulation with CDA or 2′3′-cGAMP did not alter the expression of surface markers (CD47, EGFR, PD-L1, CD80, HLA-A2 and HLA-DR) on HNSCC cell lines (Supplementary Fig. S2), showing a gross defect in the activation of this pathway.