Pleural mesothelioma: an approach to diagnostic problems

In the 1960s, a close relationship between heavy exposures to crocidolite asbestos and mesothelioma was established. The debate on the diagnosis of mesothelioma became complicated because of the possibility of litigation. Well differentiated mesothelioma cells are mucicarmine negative but alcian blue and periodic acid-Schiff (PAS) positive, which are removed by hyaluronidase and diastase digestion. By electron microscopy (EM), they show bush-like elongated, slender, and branching microvilli. By immunohistochemistry they express both keratin and vimentin but not carcinoembryonic antigenicity (CEA), B72.3, Ber-EP4, and Leu-M1. In poorly differentiated mesotheliomas, chromosomal and molecular biological alterations are common and complex but these alterations also overlap with that of poorly differentiated tumours of the lung and other organs. A poorly differentiated pleural tumour is most likely metastatic and needs good team work to locate the primary site. The diagnosis of a mesothelioma and asbestosis should be established separately. Future studies will be focused less on the phenotypic differences but more on the broad molecular and multi-phasic mechanisms of carcinogenesis, irrespective of the aetiological agents, in poorly differentiated tumours.