“…In NE tumors, conventional immunohistochemical panels used for adenocarcinoma metastases of unknown origin adenocarcinoma are less useful. As recently described, a panel including TTF‐1, CDX2, GATA‐3, SATB2, and progesterone receptors is recommended to rule out a pulmonary, digestive, mammary, urothelial, and pancreatic origin 4 (Table S1). In our case, the immunohistochemical study was key to identifying the rectal origin of the neoplasm, and establish the differential diagnosis with MCC, with negativity for CK20, TTF‐1, and neurofilament and positivity for CDX2.…”