Resistance to osimertinib including on-target mechanisms such as novel EGFR secondary mutation, off-target mechanisms such as mesenchymal-epithelial transition or human EGFR 2 amplification, mutations in downstream signaling molecules, and oncogenic fusions, and the Histological transformations (such as epithelial-mesenchymal transition, squamous cell carcinoma, or small cell lung cancer) have been well described. Here, EGFR is linked to small cell lung carcinoma.