The patient-derived cell line KPP-03 with high AXL expression was insensitive to EGFR TKIs. (A) The AXL mRNA expression levels of KPP-03, PC-9, and HCC827 cells measured by the qPCR assay. (B) The indicated proteins of KPP-03, PC-9, and HCC827 cells detected by the Western blotting assay. (C) KPP-03, PC-9, and HCC827 cells were incubated with erlotinib plus ramucirumab (150 ng/μL) or osimertinib for 72 hours. Cell viability was determined using the MTT assay. (D) KPP-03, PC-9, and HCC827 cells treated with nonspecific control or AXL-specific siRNA were incubated with or without erlotinib (100 nmol/L) or osimertinib (100 nmol/L) for 72 hours, and cell viability was detected using MTT assays. p-, phosphorylated-; qPCR, quantitative polymerase chain reaction; si, small interfering.