In many cases, expression of mutated gene in a cancer is tested before starting any therapy: the mutation of EFGR should be tested in all patients with NSCLC prior to start any systemic therapy and the presence of T790M resistance mutation, targetable by osimertinib, should be tested in patients with disease progression after first-line therapy with an EGFR inhibitor (Fig. 11). This evidence concerns the gene EGFR and non-small cell lung carcinoma.