Solid carcinomas of the stomach. A combined histochemical, light and electron microscopic study.

Twenty cases of solid carcinoma of the stomach (SCS) were studied light and electron microscopically and histochemically. On the histologic, histochemical, and ultrastructural bases they were divided into three subgroups: mucin-secreting carcinomas (MSC) (12 cases); neuroendocrine tumors (NET) (five cases); and composite tumors (CT) (three cases). Histochemically, mucin was detectable at high intensity in most cases of MSC and ultrastructurally, the mucin granules, the number of which varied considerably from cell to cell, showed prominent pleomorphism with varying degree of maturity. Uniformly round neuroendocrine granules were demonstrable in all of the NET cases and in two cases of CT. The argyrophilic stain was negative in two cases of NET, whereas it was positive in three cases of MSC. Thus, there was a discrepancy between the silver nitrate reduction intensity and the ultrastructural demonstrability of neuroendocrine granules. Histologically, combined occurrence of some nuclear palisading of basal cells and rosette-like arrangement without evident glandular formation was specific to NET and this provides a helpful basis for the light microscopic differentiation of this tumor from other type tumors.