SFTPC and adenocarcinoma: Due to the presence of papillary structures located at the bronchiole/alveoli border at the end of a stretch of club cells, which express both the club cell marker CC10 and the AT2 cell marker SPC, the authors suggested a model in which KrasG12D promoted the transdifferentiation of club cells into CC10–SPC-double-positive cells, which serve as the cell of origin of lung adenoma and adenocarcinoma (Jackson et al. 2001).