EGFR exon 20 T790M deletion, which occurs in 50–60% of NSCLC patients undergoing first-generation EGFR-TKI therapy (such as erlotinib or gefitinib), is the most common mechanism of acquired resistance; the second generation of EGFR-TKI (afatinib and dacomitinib) was developed aiming to circumvent this drawback without noticeable success [131]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.