It has been reported that 60% of mucinous bronchioloalveolar carcinoma cases showed CK7 + / CK20 + and that it is difficult to distinguish mucinous bronchioloalveolar carcinoma from mucinous colorectal adenocarcinoma metastatic to the lung based on the CK7 and CK20 phenotype [32]. The gene discussed is KRT20; the disease is colorectal mucinous adenocarcinoma.