Praktische Differenzialdiagnose präneoplastischer Veränderungen der Pleura und früher mesothelialer Neoplasien

[Mesothelial proliferation of the tunica vaginalis testis]

Proliferative changes seen in reactive mesothelial hyperplasia of a hydrocele sac may mimic malignant mesothelioma. There is no immunohistochemical staining that reliably separates benign from malignant mesothelial proliferations. However, the combined analysis of BAP1 by immunohistochemistry and CDKN2A by FISH has been reported to yield both a high specificity and sensitivity in this differential diagnosis. In addition, the evaluation of risk factors such as asbestos exposure or prior traumata may be helpful for the correct diagnosis. Exclusion of stromal invasion, which is diagnostic for malign mesothelioma, is of utmost importance. Therefore, extended histological workup is essential.

[Morphological diagnostics of malignant pleural mesothelioma]

The World Health Organization (WHO) classification differentiates between pleural tumors of mesothelial and mesenchymal origin as well as lymphoproliferative disorders, with malignant mesotheliomas forming the most common pleural primary tumor. Histologically, epithelioid (40-60 %), sarcomatoid (20-40 %), and biphasic mesotheliomas (20-40 %) are distinguished. The certain morphological diagnosis of a malignant pleural mesothelioma requires the establishment of mesothelial differentiation by means of an appropriate panel of antibodies to exclude pleural dissemination of a pulmonary or extrapulmonary epithelial malignancy and also requires the establishment of at least focal invasive growth to distinguish from reactive mesothelial proliferation. The exclusion of a malignant pleural mesothelioma may induce further differential diagnostic considerations, e. g. concerning the assignment to a certain primary tumor after the establishment of carcinomatous pleuritis.

Immunohistochemistry and Molecular Diagnostics of Pleural Malignant Mesothelioma

Context.—The pathologic approach to pleural-based lesions is stepwise and uses morphologic assessment, correlated with clinical and imaging data supplemented by immunohistochemistry (IHC), and more recently, molecular tests, as an aid for 2 main diagnostic problems: malignant mesothelioma (MM) versus other malignant tumors and malignant versus reactive mesothelial proliferations.

Objective.—To present the current knowledge regarding IHC and molecular tests with respect to MM diagnosis, and in particular, the differentiation of the epithelioid type of MM from carcinoma metastatic to the pleural cavity.

Data Sources.—A review of immunohistochemical features of 286 consecutive MMs from 459 cases of pleural pathology, diagnosed during routine practice from 2003 to 2009. A survey of biomedical journal literature from MedLine/PubMed (US National Library of Medicine) focused on MM and associated tissue-based diagnostic IHC markers and molecular tests.

Conclusions.—The search for a single diagnostic marker of MM has so far been discouraging, given the biologic and phenotypic tumor heterogeneity of MM. The use of antibody panels has gained unanimous acceptance especially in the differential diagnosis between MM and metastatic carcinoma, whereas the usefulness of IHC is more limited when dealing with spindle cell malignancies or distinguishing malignant from reactive mesothelium. A great degree of interlaboratory variability in antibody combinations and clone selection within diagnostic panels still exists. Current investigations aim at selecting the most suitable and cost-effective combination of antibodies by using novel statistical approaches for assessing diagnostic performance beyond the traditional measures of sensitivity and specificity.