ULTRASTRUCTURE OF HUMAN MALIGNANT DIFFUSE MESOTHELIOMA

Abstract

Eleven cases of malignant diffuse mesotheliomas, histologically classified into 2 groups, epithelia (5 pleural and 3 peritoneal) and biphasic or mixed (2 pleural and 1 peritoneal) forms, were studied by EM to elucidate their ultrastructural characteristics. The neoplastic cells of the epithelial forms were varied in ultrastructure, from well differentiated (marked by polarity, microvilli, glycogen granules, junctional structures, tonofilaments, intracellular vacuoles and a basement membrane) to poorly differentiated (which lacked some of these epithelial characteristics). In 4 of 8 instances in epithelial tumors, nonepithelial or mesenchymal neoplastic cells were recognized. The biphasic or mixed cases included 3 major cell types: epithelial, atypical epithelial and mesenchymal. It appeared that there were transitional forms among the 3 cells types. The observations support the concept that the neoplastic cell of malignant mesothelioma can differentiate into a number of cell lines.