Abstract
BACKGROUND: Solid predominant lung adenocarcinomas (LUAD) have distinct histopathological and clinical characteristics compared with nonsolid subtypes. A comprehensive comparison of altered genes found in solid and nonsolid subtypes has not previously been performed. In this study, we analyzed differences in gene expression, genetic mutations, and DNA methylation to better understand the risk factors for these two subtypes of LUAD. METHODS: Differentially expressed genes (DEGs) and differentially mutated genes (DMGs) were analyzed from RNA-seq data downloaded from The Cancer Genome Atlas (TCGA) and Broad Institute database. To understand the functional significance of molecular changes, we examined the DEGs and DMGs with Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis. RESULTS: A total of 184 patients in the TCGA cohort and 140 patients in the Broad Institute cohort were included in this study. We identified 75 DEGs, of which 15 were upregulated and 56 downregulated in the solid group relative to the nonsolid group. The DEGs were mainly involved in the regulation of water and fluid transport. We discovered 38 significantly differentially expressed genes that overlapped in the two groups. The DMGs were mainly enriched for pathways involved in cell-cell adhesion, cell adhesion, biological adhesion, and hemophilic cell adhesion. We additionally discovered nine significantly methylated genes between solid and nonsolid LUAD. CONCLUSIONS: Our study identified distinct DEGs, DMGs, and methylation genes for solid and nonsolid LUAD subtypes. These findings improve our understanding of the different carcinogenesis mechanisms in LUAD and will help to develop new therapeutic strategies.