STAT3 and lung carcinoma: In vitro studies of EGFR-mutant lung cancer have shown that the expression of PD-L1 is increased in these cancer cells through downstream effectors in the EGFR pathway, such as STAT3 (signal transducer and activator of transcription 3) and ERK1/2 (extracellular signal-regulated kinase 1/2) [18–20].