EGFR and non-small cell lung carcinoma: As they proliferate NSCLC cells can acquire or intrinsically possess mutational changes that make them resistant to first- and second-generation EGFR-TKIs.27 One recognized mechanism of resistance is the insertion of additional base pairs in exon 20 that adds 1–7 additional amino acids to the structure of the EGFR, called exon 20 insertion mutations (EGFR ex20ins).