Desmin and neural marker expression in mesothelial cells and mesotheliomas

The distribution of keratin, vimentin, desmin, muscular actin, S100, specific neuron enolase, and chromogranin was studied by immunoperoxidase staining in mesothelium, malignant mesotheliomas, and pulmonary carcinomas. The mesothelial cells were positive for keratin and vimentin on all smears of pleural and ascitic effusions; most of them were also positive for desmin but rarely for enolase and S100. None was positive for muscular actin. Sixteen malignant mesotheliomas expressed vimentin and keratin; six were also positive for desmin, three for desmin and neural markers, and five for neural markers. In comparison, none of the pulmonary carcinomas was positive for these markers. Mesothelial cells are able to express markers of divergent differentiation. Mesotheliomas also have such markers that are present in other malignant tumors and, in particular, in intra-abdominal desmoplastic small cell tumors with divergent differentiation. This entity and mesotheliomas probably originate from the same cell. Moreover, desmin, found in 56% of malignant mesotheliomas but absent in pulmonary carcinomas, may be useful in the differential diagnosis of these tumors.