EGFR and non-small cell lung carcinoma: To clarify the expression status of PD-L1 in EGFR-TKIs resistant NSCLC and determine why PD-L1 expression in the tumours of these patients changed after acquired EGFR-TKIs resistance, we collected specimens from 15 NSCLC patients who acquired EGFR-TKI resistance (Additional file 2: Table S1) and detected PD-L1 expression via PD-L1 IHC 22C3 pharmDx.