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Two localized and two diffuse pulmonary mesotheliomas were studied with both light and electron microscopes. The diffuse mesotheliomas showed features and characteristics of mesothelial cells in the electron microscope, whether lining spaces or within solid parts of the tumor. The localized mesothelioma showed predominance of poorly differentiated cells and fibroblasts. The relationship between the localized and diffuse mesotheliomas is not clear, but the former could be a group of variegated tumors. It appears that a definite electron microscopic diagnosis of diffuse pulmonary mesothelioma can be made at least in some of the surgically removed tissues suspected to be diffuse mesothelioma by clinical and light microscopic findings.
Nai‐San Wang (Tue,) studied this question.