NTRK1 and non-small cell lung carcinoma: Notably, structurally analogous exon 20 insertion mutations that can promote ligand-independent activation that are also found in HER2, another member of the EGFR family of receptor tyrosine kinases (RTK).23,31 Although HER2 mutations are present at a much lower frequency (~2% of NSCLC patients) compared with EGFR mutations, exon 20 insertions are, by far, the most dominant type of HER2 aberration in NSCLC, representing greater than 90% of all observed HER2 mutations.32,33