Several mechanisms of resistance to osimertinib have been reported in EGFR T790M-positive NSCLC patients, such as acquired C797S mutation, maintained T790M mutation without acquired C797S mutation, loss of T790M mutation despite the presence of the underlying EGFR activating mutation, loss of EGFR-mutant clones plus alternative pathway activation or histologic transformation, EGFR ligand-dependent activation, and human EGFR-2 and MET amplification [12–14]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.