STAT3 and non-small cell lung carcinoma: There have been studies supporting the theory that PD-L1 is a downstream molecule of EGFR signaling and EGFR-TKI could down-regulate PD-L1 expression on NSCLC cells by pathways like IL-6/JAK/STAT3, NKκB, or p-ERK1/2/p-c-Jun (36–38).