Instead, the markers for club cells, bronchioalveolar stem cells and basal cells, which represent the other candidate origins of lung tumors, such as Scgb1a1 and Krt5 either decreased or maintained their normal expression in Med23−/− lung tumors (Figure 1I,J).[24, 25, 26] Moreover, Med23−/‐ lung tumors primarily exhibited histologic phenotype of adenocarcinoma instead of papillary carcinoma which has a high number in the CC10+ cells‐derived lung cancer (Figure 1G,K).[25] Taken together, these results largely demonstrated that Med23−/− lung tumor is the AT2 cell‐derived lung adenocarcinoma. This evidence concerns the gene KRT5 and lung cancer.