Development of tumors in the glandular stomach of rats after oral administration of carcinogens. II. Different cell types in antral carcinoma as revealed by electron microscopy.

In the present study electron microscopic investigations of tumors of the glandular stomach of rats induced by oral administration of MNNG or ENNG are dealt with. The aim of the study was to describe the different cell types found in the carcinoma and to elucidate the possible relationship between the undifferentiated carcinoma cells and the more differentiated cell types found in the tumor. The results show that besides undifferentiaded carcinoma cells, several differentiated cell types such as goblet cells, endocrine cells, cells with lamellated inclusions in their cytoplasm, and squamous carcinoma cells can be observed. The most conspicuous findings were carcinomatous gland cells with well differentiated microvilli on their luminal surface and typical tonofilamentous structures in their cytoplasm. These cells exhibited signs of the squamous epithelium and of gland cells. Therefore they may be considered as intermediate variants between adenocarcinoma cells and squamous carcinoma cells. The occurrence of such intermediate steps points to the possibility of differentiation by cell division of adenocarcinoma cells into several metaplastic cell types in the experimental stomach carcinoma induced by MNNG or ENNG.