Approximately 70% of patients whose lung cancers
harbour somatic mutations in exons encoding the tyro-
sine kinase domain of the epidermal growth factor
receptor (EGFR) will experience significant tumour
regressions when treated with EGFR tyrosine kinase
inhibitor (TKI) gefitinib or erlotinib.
1
However, the
overwhelming majority of these patients inevitably
develop acquired resistance to either drug. To date, sev-
eral major mechanisms of acquired resistance, such as
secondary mutation of the EGFR gene, amplification
of mesenchymal–epithelial transition (MET) gene and
overexpression of hepatocyte growth factor (HGF),
have been reported and advances in the development
of effective pharmaceutical agents against these mecha-
nisms are being made.
2
EGFR gene mutations such as
exon 20 insertion and KRAS gene mutation are believed
to contribute to primary resistance to EGFR-TKI
treatment