Since the tumor nodules in Rnf43−/−; KrasG12D lungs were positive for duct marker CK19 and negative for pulmonary adenocarcinoma marker thyroid transcription factor 1 (TTF‐1) (Figure 4D,E), they are likely to be metastatic PDAC but not spontaneous lung tumor. Here, NKX2-1 is linked to neoplasm.