Gastrointestinal carcinoid tumours: histological, histochemical and immunohistochemical study.

The histological, histochemical and immunohistochemical features of twenty gastrointestinal carcinoid tumours are presented. Histologically, the foregut and hindgut carcinoids showed trabecular pattern and midgut carcinoid tumours usually showed insular type of growth. Histochemically, using the silver stains by the Grimelius and Masson-Fontana techniques, most (18 cases) were argyrophilic and 8 were argentaffin positive. Two appendiceal carcinoids were non-reactive. Mucin positivity was noted in a case of mucin producing carcinoid of the appendix. Immunohistochemistry for wide spectrum keratin, cytokeratin PKK1, carcinoembryonic antigen, neuron-specific enolase, neurofilament and S-100 protein revealed epithelial and neural characteristics of carcinoid tumour cells. Wide spectrum keratin was positive in 12 while cytokeratin PKKI was negative in all. Carcinoembryonic antigen positivity was noted in 8 cases. Neuron-specific enolase immunoreactivity was seen in 18 cases whereas neurofilament was negative. S-100 protein positive cells were observed in close contact with and/or intermingled with tumour cells but the tumour cells themselves were negative. Immunoreactivity for somatostatin was seen in 8 cases, glucagon in three, and corticotrophin, insulin and gastrin in one case each. More than one hormone expression was noted in three cases, one each of gastric, appendiceal and rectal carcinoid tumours. These findings suggest that carcinoid tumours may develop from an uncommitted cell native to the site of tumour and differentiates along one or more directions, and the immunohistochemical findings and secretory profile of these tumour cells depend upon the direction of their differentiation.