Focal parietal cell differentiation in a well-differentiated (intestinal-type) early gastric cancer.

A well-differentiated (intestinal-type) early gastric cancer characterized by multifocal areas containing adenocarcinoma cells with eosinophilic cytoplasm is presented. The electron microscopy revealed that cytoplasmic eosinophilia was mainly due to the presence of numerous mitochondria. In addition, individual cells showed features of preparietal cell differentiation such as numerous mitochondria, tubulovesicles, intracellular canaliculi and rare mucin granules. There were also adenocarcinoma cells with a pyloric gland (mucopeptic) differentiation as revealed by the presence of granules with a dense protein core eccentrically located in the mucus matrix. These ultrastructural data suggested a gastric epithelial cell differentiation. The implications with regard to the classification and histogenesis of this tumor are discussed.