The mechanisms underlying resistance to osimertinib, a third-generation EGFR-TKI, have been investigated [46,47], and the presence of the EGFR C797S mutation in addition to the T790M mutation (T790M/C797S double-positive) has been proposed as one of the main mechanisms responsible for resistance acquisition in T790M mutation-positive lung cancer [48]. The gene discussed is EGFR; the disease is lung cancer.