Purpose: Lung adenocarcinoma often manifests as tumors with mainly lepidic growth. The size of invasive foci determines a diagnosis of in situ, minimally invasive adenocarcinoma, or invasive types and suggests that some adenocarcinomas undergo malignant progression in that order. This study investigates how transcriptional aberrations in adenocarcinoma cells at the early stage define the clinical phenotypes of adenocarcinoma tumors at the advanced stage.
Experimental design: We comprehensively searched for differentially expressed genes between preinvasive and invasive cancer cells in one minimally invasive adenocarcinoma using laser capture microdissection and DNA microarrays. We screened expression of candidate genes in 11 minimally invasive adenocarcinomas by reverse transcriptase PCR and examined their involvement in preinvasive-to-invasive progression by transfection studies. We then immunohistochemically investigated the presence of candidate molecules in 64 samples of advanced adenocarcinoma and statistically analyzed the findings, together with clinicopathologic variables.
Results: The transcription factors Notch2 and Six1 were upregulated in invasive cancer cells in all 11 minimally invasive adenocarcinomas. Exogenous Notch2 transactivated Six1 followed by Smad3, Smad4, and vimentin, and enlarged the nuclei of NCI-H441 lung epithelial cells. Immunochemical staining for the transcription factors was double positive in the invasive, but not in the lepidic growth component of a third of advanced Ads, and the disease-free survival rates were lower in such tumors.
Conclusions: Paired upregulation of Notch2 and Six1 is a transcriptional aberration that contributes to preinvasive-to-invasive adenocarcinoma progression by inducing epithelial-mesenchymal transition and nuclear atypia. This aberration persisted in a considerable subset of advanced adenocarcinoma and conferred a more malignant phenotype on the subset.
©2011 AACR.