Analysis of Epidermal Growth Factor Receptor Gene Mutation in Patients with Non–Small Cell Lung Cancer and Acquired Resistance to Gefitinib

Abstract

Purpose: Non^small cell lung cancers carrying activating mutations in the gene for the epidermal growth factor receptor (EGFR) are highly sensitive to EGFR-specific tyrosine kinase inhibitors. However, most patients who initially respond subsequently experience disease progression while still on treatment. Part of this ''acquired resistance'' is attributable to a secondary mutation resulting in threonine to methionine at codon 790 (T790M) of EGFR. Experimental Design: We sequenced exons 18 to 21of the EGFR gene to look for secondary mutations in tumors with acquired resistance to gefitinib in 14 patients with adenocarcinomas. Subcloning or cycleave PCR was used in addition to normal sequencing to increase the sensitivity of the assay. We also looked for T790M in pretreatment samples from 52 patients who were treated with gefitinib. We also looked for secondary KRAS gene mutations because tumors with KRAS mutations are generally resistant to tyrosine kinase inhibitors. Results: Seven of 14 tumors had a secondary T790M mutation. There were no other novel secondary mutations. We detected no T790M mutations in pretreatment specimens from available five tumors among these seven tumors. Patients with T790M tended to be women, never smokers, and carrying deletion mutations, but the T790M was not associated with the duration of gefitinib administration. None of the tumors had an acquired mutation in the KRAS gene. Conclusions: A secondary T790M mutation of EGFR accounted for half the tumors with acquired resistance to gefitinib in Japanese patients. Other drug-resistant secondary mutations are uncommon in the EGFR gene.

The epidermal growth factor receptor family: Biology driving targeted therapeutics

“…In NSCLCs with mutant EGFR, a common exon 20 missense mutation (T790M) within the tyrosine kinase domain of mutant EGFR is responsible for TKI resistance in approximately 50 % of cases [183][184][185]. Also, point mutations in the ATP-binding pocket of HER-2/Neu may significantly impair the response of breast cancer cell lines to gefitinib [186].…”

Overview of molecular testing in non-small-cell lung cancer: mutational analysis, gene copy number, protein expression and other biomarkers of EGFR for the prediction of response to tyrosine kinase inhibitors

“…A secondary mutation involving the substitution of methionine for threonine in codon 790 (T790M) is present in approximately 50% of cases of acquired resistance (Kobayashi et al, 2005;Pao et al, 2005a;Kosaka et al, 2006;see Gazdar, 2009). Screening for the emergence of the T790M mutation during treatment may allow for the earlier identification of acquired resistance.…”

The Role of MET Activation in Determining the Sensitivity to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors

“…However, resistance to these drugs invariably develops, and this limits median response duration to 6 to 8 months, although therapeutic response can sometimes persist for more than 2 years (3). Studies undertaken to elucidate the mechanism underlying acquired resistance found that the secondary T790M mutation is an important contributory factor in up to 50% of cases (4,5). MET amplification was recently found to be involved in escape from the anticancer effects of EGFR inhibitors (6).…”