EGFR and neoplasm: The PC‐9/GR cell is a gefitinib‐acquired resistant cell subline of PC‐9 cells, which has an EGFR‐activating mutation, which is a 15‐bp deletion in the EGFR exon 19 and is initially sensitive to gefitinib.18 The gefitinib resistance mechanism is very complex, may relate to secondary mutation of EGFR, c‐Met amplification, compensatory signal establishment and the change in regulatory factors expression and the tumour microenvironment transformation.