The high post-test probability of a cytological examination renders further investigations to establish a diagnosis of epithelial malignant pleural mesothelioma redundant

The aim of the study was to establish in a prospective and blinded manner the diagnostic yield of morphology, immunocytochemistry (ICH) and electron microscopy (EM) in the cytological analysis of malignant pleural mesothelioma (MPM). Pleural fluid from consecutive patients, 14 with a histologically proven MPM, 12 with a malignant pleuritis due to adenocarcinoma (AC), and 13 with a reactive pleural effusion (RM),,was separately analyzed. Smears were incubated with monoclonal antibodies (Tag72, Ber-Ep4, anti-CEA, EMA). These were considered suggestive for MPM when only EMA stained positive, for AC when three out of four markers stained positive, and for RM when no marker stained positive. The post-test probability of the morphological, ICH, and EM analysis were 92, 100, 92% or MPM, 91, 100, 86% for AC, and 88, 88, 90% for RM, respectively. We concluded that the high post-test probability of a combined morphological and ICH diagnosis of MPM warrants to cease further diagnostic procedures in these patients. Electron microscopy did not add to accuracy of diagnosis.