Immunohistochemistry showed positive expression of cytokeratin 7 (CK7) (Figure 3) and negative expression of cytokeratin 20 (CK20) (Figure 4), typical for primary lung adenocarcinoma (CK7+ / CK20−) and ruling out metastatic colonic carcinoma to the lung (CK7−/ CK20+)6. The gene discussed is KRT20; the disease is lung adenocarcinoma.