Lung epithelial cells as cells of origin of lung cancer. Different epithelial cell types line the epithelium of the different regions of the lung, the bronchiolar epithelium, the bronchioalveolar duct junction (BADJ) and the alveolar space. PNECs have been shown to be the cell of origin for small cell lung carcinoma (SCLC) and large cell lung carcinoma (LCC); basal cells, club cells and AT2 cells can give rise to squamous cell carcinoma (SqCC). AT2 cells are a confirmed cell of origin for lung adenocarcinoma (LUAD), whilst ciliated cells, goblet cells and bronchioalveolar stem cells (BASCs) are suspected to be able to give rise to LUAD in specific conditions (dotted lines). There is no evidence for AT1 cells as a cell of origin for lung cancer.