SOX2 and adenocarcinoma: Given that the embryonic stem cell SOX2 transcriptional factor [7] plays important roles in tracheal epithelial cells [8] and is only expressed in the main airways and non-branching bronchioles in the developing and adult mouse lung [9], we hypothesized that it may be a cell-lineage gene highly and specifically expressed in SCCs that originate from central and upper airway and bronchial epithelial cells relative to adenocarcinomas that typically arise from the lung periphery [10].