IMMUNOHISTOCHEMICAL DIFFERENCES BETWEEN HYALURONAN-PRODUCING AND NON-HYALURONAN-PRODUCING MALIGNANT MESOTHELIOMA

In many but not all cases, malignant mesothelioma is associated with a n elevated content of hyaluronan in pleural fluid, The hyaluronan-prod ucing mesothelioma has not yet been immunohistochemically characterize d; therefore, the purpose of this study was to compare the immunohisto chemical reactivity patterns in relation to the ability of this tumour to produce hyaluronan. Pleural fluid samples from 33 patients with ma lignant mesothelioma were analysed for content hyaluronan using a quan titative high performance liquid chromatographic graphic method, Biops y specimens from the patients were studied immunohistochemically, usin g monoclonal antibodies against carcinoembryonic antigen (CEA), epithe lial membrane antigen (EMA), a low molecular weight cytokeratin antige n (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 t he monoclonal antibody raised against CEA in any case, There was a sig nificantly 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 le vels of hyaluronan. Mesotheliomas that produced hyaluronan differed im munohistochemically from those that did not. The connection between th e ability to produce different antigens and hyaluronan may relate to t he degree of differentiation of the tumour. Both of these characterist ics (immunophenotype and ability to produce hyaluronan) may, therefore , be of importance in studies concerning the prognosis and treatment o f the malignant mesothelioma.