Malignant vascular tumours of the pleura in "asbestos" workers and endothelial differentiation in malignant mesothelioma

Background-Three cases of diffuse malignant vascular tumours of the pleura are described which mimicked malignant mesothelioma clinically and patholog ically (so called "pseudomesothelioma"). All had occupational histories of exposure to asbestos. The relationship of these tumours to mesothelioma and asbestos exposure is discussed. Methods-To examine the histogenetic relationship between mesothelioma and t hese three tumours an immunohistochemical analysis of vascular marker (CD31 , CD34, and Von Willebrand factor) expression was undertaken in 92 cases of pleural mesothelioma, in addition to these three tumours. Electron microsc opic fibre analysis of lung tissue was performed on each of the three cases to assess asbestos fibre content. Results-Diffuse pleural epithelioid haemangioendotheliomas may closely rese mble malignant mesothelioma clinically and pathologically but, of the 92 pl eural mesotheliomas tested, none showed expression of CD31, CD34, and Von W illebrand factor. Although all three cases had claimed exposure to asbestos , ferruginous bodies typical of asbestos were only seen by light microscopy in case 2, and only in this subject was the asbestos fibre content raised in comparison with the range seen in a non-exposed background population. T he latent period in the pleural epithelioid haemangioendotheliomas ranged f rom 18 to 60 years. Conclusions Endothelial differentiation does not appear to occur in mesothe lioma and therefore should be clearly separated from it. No definite associ ation between pleural epithelioid haemangioendothelioma and exposure to asb estos can be made from this small series but further investigation is warra nted.