However, due to the fact that after a good initial response to first-generation TKIs, non–small cell lung cancer (NSCLC) patients with EGFR-activating mutations (in particular T790M) ultimately undergo disease progression, it has been necessary to develop a novel, irreversible EGFR TKI that features selectivity against sensitizing and T790M-resistant mutant forms versus wild-type forms of EGFR. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.