HISTOCHEMICAL AND ULTRASTRUCTURAL ANALYSES OF GLANDULAR DIFFERENTIATION IN TYPICAL CARCINOID-TUMOR OF THE HINDGUT

Adenomatous differentiation of typical carcinoid tumors was examined b y histochemical and ultrastructural studies on 33 cases of typical car cinoids of the hindgut. Of these 33 carcinoids, 12 (36%) showed a tubu lar and/or acinar pattern with production of mucus as a minor componen t. A few tumor cells with mucous globules were scattered among tubules in these carcinoids. Ultrastructurally, microvilli were seen along th e luminal surface of tubules, with both numerous mucous globules in th e supranuclear area and endocrine granules in basal sites of the same cells. These results indicate that even in typical carcinoid tumors, c ertain tumor cells have the features of goblet cells or the open type of endocrine cells. The findings of both mucous globules and endocrine granules in the same single cells indicate a close relationship betwe en endocrine cells and mucus-producing and/or tubule-forming cells. It is concluded that pluripotential cells producing carcinoid tumors mig ht be able to differentiate into three types of tumor cells: (i) endoc rine cells without microvilli or mucus production; (ii) cells with mic rovilli and no mucus product; and (iii) mucus-containing cells with mi crovilli.