MUC5AC and mucinous adenocarcinoma: In areas of the appendiceal wall, the nests of signet ring cells coalesced into pools of mucin containing “floating” cells, indicating frank mucinous carcinoma, so-called adenocarcinoma ex-goblet cell carcinoid (Fig. 5), Tang group B. Immunohistochemistry for synaptophysin highlighted scattered occasional peripheral endocrine cells, as is characteristic of goblet cell carcinoid (Fig. 6).