KRT20 and neoplasm: Immunohistochemically, tumor cells were positive for cytokeratin (CK)-AE1/3, CK7, TTF-1 (Fig. 5b), CEA (Fig. 5c), calcitonin (Fig. 5d), synaptophysin, and chromogranin A, but negative for CK20, Napsin A, Pax8, and p40.