EGFR and non-small cell lung carcinoma: There are mainly two mechanisms of de novo resistance that have been described so far in NSCLC: The first one involves drug resistant EGFR mutations (e.g. exon 20 mutants or rare mutations such as D761Y or T790M occurring in cis with an activating EGFR mutation), and the second includes other genetic alternations that co-occur with an EGFR-activating mutation in NSCLC tumours.