Lung Cancer: Understanding Its Molecular Pathology and the 2015 WHO Classification

Mutations in the tyrosine kinase (TK) domain of the epidermal growth factor receptor (EGFR) gene in lung cancers are associated with increased sensitivity of these cancers to drugs that inhibit EGFR kinase activity. However, the role of such mutations in the pathogenesis of lung cancers is unclear. We sequenced exons 18-21 of the EGFR TK domain from genomic DNA isolated from 617 non-small-cell lung cancers (NSCLCs) and 524 normal lung tissue samples from the same patients and 36 neuroendocrine lung tumors collected from patients in Japan, Taiwan, the United States, and Australia and from 243 other epithelial cancers. Mutation status was compared with clinicopathologic features and with the presence of mutations in KRAS, a gene in the EGFR signaling pathway that is also frequently mutated in lung cancers. All statistical tests were two sided. We detected a total of 134 EGFR TK domain mutations in 130 (21%) of the 617 NSCLCs but not in any of the other carcinomas, nor in nonmalignant lung tissue from the same patients. In NSCLC patients, EGFR TK domain mutations were statistically significantly more frequent in never smokers than ever smokers (51% versus 10%), in adenocarcinomas versus cancer of other histologies (40% versus 3%), in patients of East Asian ethnicity versus other ethnicities (30% versus 8%), and in females versus males (42% versus 14%; all P < .001). EGFR TK domain mutation status was not associated with patient age at diagnosis, clinical stage, the presence of bronchioloalveolar histologic features, or overall survival. The EGFR TK domain mutations we detected were of three common types: in-frame deletions in exon 19, single missense mutations in exon 21, and in-frame duplications/insertions in exon 20. Rare missense mutations were also detected in exons 18, 20, and 21. KRAS gene mutations were present in 50 (8%) of the 617 NSCLCs but not in any tumors with an EGFR TK domain mutation. Mutations in either the EGFR TK domain or the KRAS gene can lead to lung cancer pathogenesis. EGFR TK domain mutations are the first molecular change known to occur specifically in never smokers.

The EML4-ALK fusion oncogene represents a novel molecular target in a small subset of non-small-cell lung cancers (NSCLC). To aid in identification and treatment of these patients, we examined the clinical characteristics and treatment outcomes of patients who had NSCLC with and without EML4-ALK. Patients with NSCLC were selected for genetic screening on the basis of two or more of the following characteristics: female sex, Asian ethnicity, never/light smoking history, and adenocarcinoma histology. EML4-ALK was identified by using fluorescent in situ hybridization for ALK rearrangements and was confirmed by immunohistochemistry for ALK expression. EGFR and KRAS mutations were determined by DNA sequencing. Of 141 tumors screened, 19 (13%) were EML4-ALK mutant, 31 (22%) were EGFR mutant, and 91 (65%) were wild type (WT/WT) for both ALK and EGFR. Compared with the EGFR mutant and WT/WT cohorts, patients with EML4-ALK mutant tumors were significantly younger (P < .001 and P = .005) and were more likely to be men (P = .036 and P = .039). Patients with EML4-ALK-positive tumors, like patients who harbored EGFR mutations, also were more likely to be never/light smokers compared with patients in the WT/WT cohort (P < .001). Eighteen of the 19 EML4-ALK tumors were adenocarcinomas, predominantly the signet ring cell subtype. Among patients with metastatic disease, EML4-ALK positivity was associated with resistance to EGFR tyrosine kinase inhibitors (TKIs). Patients in the EML4-ALK cohort and the WT/WT cohort showed similar response rates to platinum-based combination chemotherapy and no difference in overall survival. EML4-ALK defines a molecular subset of NSCLC with distinct clinical characteristics. Patients who harbor this mutation do not benefit from EGFR TKIs and should be directed to trials of ALK-targeted agents.

Histopathology is insufficient to predict disease progression and clinical outcome in lung adenocarcinoma. Here we show that gene-expression profiles based on microarray analysis can be used to predict patient survival in early-stage lung adenocarcinomas. Genes most related to survival were identified with univariate Cox analysis. Using either two equivalent but independent training and testing sets, or 'leave-one-out' cross-validation analysis with all tumors, a risk index based on the top 50 genes identified low-risk and high-risk stage I lung adenocarcinomas, which differed significantly with respect to survival. This risk index was then validated using an independent sample of lung adenocarcinomas that predicted high- and low-risk groups. This index included genes not previously associated with survival. The identification of a set of genes that predict survival in early-stage lung adenocarcinoma allows delineation of a high-risk group that may benefit from adjuvant therapy.