Cytokeratin profiles in pituitary neuroendocrine tumors

The presence and patterns of keratins are critical in the classification of pituitary neuroendocrine tumors. A large body of literature has included information about the staining patterns of pituitary tumors and tissues with the CAM 5.2 antibody. During an antibody validation for clinical use, we carried out staining of a series of 29 surgically resected pituitary cases containing 31 pituitary neuroendocrine tumors that were tested for CAM 5.2 as well as for cytokeratin (CK) 7, 18, 19, and 20 and the pan-keratin cocktail AE1/AE3. The results showed an almost identical staining pattern for CK18 and CAM 5.2; however, CAM 5.2 yielded more intense staining, whereas CK18 provided more delicate results. Staining results using AE1/AE3 were satisfactory but generally less intense; however, this marker was more specific, identifying keratin expression in one tumor that was negative with CAM 5.2. CK19 is expressed in nontumorous adenohypophysis but was less frequently positive in tumors; somatotroph and corticotroph tumors were negative for CK19, but CK19 antibody highlighted follicular cells in some gonadotroph tumors. CK7 and CK20 were negative in all pituitary tissues tested. Our findings underscore the role for CAM 5.2 and CK18 as the most valuable to identify specific alterations in adenohypophysial cells and their tumors; there is also a role for AE1/AE3 to verify the epithelial nature of pituitary neuroendocrine tumors that are negative for CAM 5.2 and CK18.