Immunohistochemically, the lesion was positive for cytokeratin-7 (CK7), focal positive for thyroid transcription factor-1 (TTF-1), and negative for cytokeratin-20 (CK20) and caudal type homeobox-2 (CDX2), which ruled out CRC metastasis (Fig. 3c, d). The gene discussed is CDX2; the disease is colorectal carcinoma.