The epidermal growth factor receptor (EGFR) kinase inhibitors gefitinib and erlotinib are effective treatments for lung cancers with EGFR activating mutations, but these tumors invariably develop drug resistance. Here, we describe a gefitinib-sensitive lung cancer cell line that developed resistance to gefitinib as a result of focal amplification of the MET proto-oncogene. inhibition of MET signaling in these cells restored their sensitivity to gefitinib. MET amplification was detected in 4 of 18 (22%) lung cancer specimens that had developed resistance to gefitinib or erlotinib. We find that amplification of MET causes gefitinib resistance by driving ERBB3 (HER3)-dependent activation of PI3K, a pathway thought to be specific to EGFR/ERBB family receptors. Thus, we propose that MET amplification may promote drug resistance in other ERBB-driven cancers as well.

Recently it has been reported that mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene occur in a subset of patients with lung cancer showing a dramatic response to EGFR tyrosine kinase inhibitors. To gain further insights in the role of EGFR in lung carcinogenesis, we sequenced exons 18 -21 of the tyrosine kinase domain using total RNA extracted from unselected 277 patients with lung cancer who underwent surgical resection and correlated the results with clinical and pathologic features. EGFR mutations were present in 111 patients (40%). Fifty-two were in-frame deletions around codons 746 -750 in exon 19, 54 were point mutations including 49 at codon 858 in exon 21 and 4 at codon 719 in exon 18, and 5 were duplications/insertions mainly in exon 20. They were significantly more frequent in female (P < 0.001), adenocarcinomas (P ‫؍‬ 0.0013), and in never-smokers (P < 0.001). Multivariate analysis suggested EGFR mutations were independently associated with adenocarcinoma histology (P ‫؍‬ 0.0012) and smoking status (P < 0.001), but not with female gender (P ‫؍‬ 0.9917). In adenocarcinomas, EGFR mutations were more frequent in well to moderately differentiated tumors (P < 0.001) but were independent of patient age, disease stages, or patient survival. KRAS and TP53 mutations were present in 13 and 41%, respectively. EGFR mutations never occurred in tumors with KRAS mutations, whereas EGFR mutations were independent of TP53 mutations. EGFR mutations define a distinct subset of pulmonary adenocarcinoma without KRAS mutations, which is not caused by tobacco carcinogens.

EGFR mutations were a good predictor of clinical benefit of gefitinib in this setting.

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.

This study has shed light on heterogeneity in lung cancers, especially in adenocarcinomas, by establishing a molecularly, genetically, and clinically relevant, expression profile-defined classification. Future studies using independent patient cohorts are warranted to confirm the prognostic significance of EGFR mutations in TRU-type adenocarcinoma.

We have previously reported that terminal-respiratory-unit (TRU) type adenocarcinoma is a distinct subset of lung adenocarcinoma in terms of molecular pathway for carcinogenesis and phenotypic profiles. This type of cancer shows TRU features, characterized by distinct cellular morphology and the expression of TTF-1 and surfactant proteins. Recently, two groups published novel mutations of the epidermal growth factor receptor (EGFR) that are closely associated with clinical response to gefitinib. The clinicopathologic features of gefitinib responders overlap with those of TRU-type adenocarcinoma, and the characteristics of TRU are likely to correspond to the bronchioloalveolar features reported as a predictor of gefitinib response. We therefore examined the characteristics of EGFR-mutated pulmonary adenocarcinomas with special reference to TRU-type adenocarcinoma. EGFR mutation was detected in 97 of 195 adenocarcinomas, 91 of 149 TRU-type adenocarcinomas and 6 of 46 tumors of other types. Conversely, 91 of 97 EGFR-mutated adenocarcinomas were categorized as TRU-type adenocarcinomas. This type-specific involvement was confirmed by logistic regression model. In addition, EGFR mutation was detected in some cases of atypical adenomatous hyperplasia, a preinvasive lesion of TRU-type adenocarcinoma. These findings further confirm that TRU-type-adenocarcinoma is a distinct adenocarcinoma subset in which a particular molecular pathway is involved.

EGFR, KRAS, and TP53 gene mutations were not independently associated with the prognosis for Japanese patients with surgically treated lung adenocarcinoma.

Introduction: MET (Met proto-oncogene) activation either by gene amplification or mutation is implicated in various types of human cancers. For lung cancer, MET gene amplification is reported to occur in a subset of adenocarcinomas. Although somatic mutations of MET in lung adenocarcinomas are rare, all but one of those reported so far entail a splice mutation deleting the juxtamembrane domain for binding the c-Cbl E3-ligase; normally such binding leads to ubiquitination and receptor degradation, and loss of this domain leads to MET activation. The purpose of this study was to clarify in the role of MET activation in lung carcinogenesis. Materials and Methods: MET gene copy number was determined by real-time quantitative polymerase chain reaction in 187 of the patients with lung cancer and the MET gene splice mutation deleting the juxtamembrane domain was examined by direct sequencing in 262. The results were correlated with various clinical and pathologic features including mutations of the epidermal growth factor receptor, KRAS, and HER2 genes. Results: All the instances of MET activation occurred in patients with adenocarcinomas. The prevalences of MET gene amplification and splice mutations were 1.4% (2 of 148) and 3.3% (7 of 211), respectively. We identified four different intronic mutations that disrupted a splice consensus sequence in genomic DNA. Activation of MET and mutations of the epidermal growth factor receptor, KRAS, and HER2 genes had strict mutual exclusionary relationships. Conclusions: About 5% of pulmonary adenocarcinomas in this cohort of Japanese patients were driven by activated MET by gene amplification or splice mutations. Such patients would be candidates for targeted therapy against MET.