CDX2 and colorectal carcinoma: PDCOs were further validated through the immunohistochemical analysis of markers that are commonly used in the differential diagnosis of CRC; CDX2, a transcription factor critical for intestinal development that is highly expressed in normal and neoplastic intestinal epithelium,15, 16 CK20, normally expressed in gastrointestinal epithelium, Merkel cells and the urothelium,17, 18 and CK7, detected in normal tissue and tumors of the lung, breast, ovary, biliary tract, and endometrium19, 20 (representative images Fig. 2b; refer also to Figure S1).