Immunohistochemical differences between hyaluronan- and non-hyaluronan-producing malignant mesothelioma.

In many but not all cases, malignant mesothelioma is associated with an elevated content of hyaluronan in pleural fluid. The hyaluronan-producing mesothelioma has not yet been immunohistochemically characterized; therefore, the purpose of this study was to compare the immunohistochemical reactivity patterns in relation to the ability of this tumour to produce hyaluronan. Pleural fluid samples from 33 patients with malignant mesothelioma were analysed for content hyaluronan using a quantitative high performance liquid chromatographic method. Biopsy specimens from the patients were studied immunohistochemically, using monoclonal antibodies against carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), a low molecular weight cytokeratin antigen (CAM 5.2) and vimentin. An elevated hyaluronan content, i.e. > 100 mg.L-1, was noted in 23 patients (70%). There was no reactivity to the monoclonal antibody raised against CEA in any case. There was a significantly higher reactivity to EMA (p = 0.026), a higher reactivity to CAM 5.2 (p = 0.053) and a lower reactivity to vimentin (p = 0.057) in the hyaluronan-producing mesotheliomas as compared to those with normal levels of hyaluronan. Mesotheliomas that produced hyaluronan differed immunohistochemically from those that did not. The connection between the ability to produce different antigens and hyaluronan may relate to the degree of differentiation of the tumour. Both of these characteristics (immunophenotype and ability to produce hyaluronan) may, therefore, be of importance in studies concerning the prognosis and treatment of the malignant mesothelioma.