EGFR and lung adenocarcinoma: To create cell line models of lung cancer patients with acquired resistance to osimertinib, we developed osimertinib resistance in the EGFR mutant osimertinib-sensitive lung adenocarcinoma cell lines, PC9, harboring the EGFRDel E746–A750 mutant, and H1975, harboring the EGFRL858R/T790M mutant by long-term culture of sensitive cells in the presence of increasing concentrations of osimertinib [20].