In this specific context, the administration of osimertinib as second line of treatment in patients harboring p.T790M mutation can re-block the tumor expansion, until additional resistance mechanisms occur as a result of the loss of the p.T790M mutation and the acquisition of novel resistance to second-line osimertinib, such as p.C797S mutation at exon 20 of EGFR (15, 34). This evidence concerns the gene EGFR and neoplasm.