Immunohistochemical analysis using cytokeratin (CK) 20, Ki-67, MUC6, and β-catenin. A and B, CK20. A, Expanded CK20 expression is noted in a hyperplastic polyp (arrow); the surrounding mucosa demonstrates normal, surface-confined
expression. B, The expanded/irregular pattern in this sessile serrated adenoma combines expanded expression with strong staining in deep
crypts (asterisks) (immunoperoxidase [IP], A, ×40; B, ×100). C and D, Ki-67. C, Expanded Ki-67 expression in this hyperplastic polyp extends nearly half-way up lesional crypts. D, The expanded/irregular pattern combines expanded expression with asymmetrical crypt staining or stretches of surface staining
(arrow) (IP, C, ×100; D, ×100). E, MUC6 expression is noted in the deep crypts of all appendiceal sessile serrated adenomas, many mixed serrated and adenomatous
lesions, and a rare hyperplastic polyp (IP, ×200). F, With β-catenin, abnormal nuclear localization is noted in a single conventional adenoma (IP, ×400). Inset, This serrated
polyp exhibits normal membranous expression (IP, ×400).