MUC5AC and mucinous cystadenoma: Group 1 is mucinous adenoma that is confined to the appendix; Group 2 is mucinous neoplasm with low-grade dysplasia that is confined to the appendix associated with extra-appendiceal acellular mucin; and Group 3 is mucinous neoplasm with low-grade dysplasia with extra-appendiceal neoplastic epithelium.