In a paper appearing in this week's PNAS Early Edition, researchers at Duke University, China's Tsingua University, and at Sage Bionetworks in Seattle identify "type II cells, Clara cells in the terminal bronchioles, and putative bronchoalveolar stem cells as cells of origin for K-Ras-induced lung hyperplasia." The team also reports that of these, "only type II cells appear to progress to adenocarcinoma."