MALIGNANT VASCULAR TUMORS OF THE SEROUS MEMBRANES MIMICKING MESOTHELIOMA - A REPORT OF 14 CASES

Malignant endothelial neoplasms involving the serous membranes are rar e, and only a few cases have been documented. We report 14 patients wi th epithelioid hemangioendothelioma (EHE) or epithelioid angiosarcoma (EA) diffusely involving the pleural, peritoneal, or pericardial cavit ies, resulting in a picture closely resembling mesothelioma. The mean age at diagnosis was 52 (range, 34-85). The patients included two wome n and one man with peritoneal tumors, eight men with pleural tumors, a nd three men with pericardial tumors. A shared histological appearance was a diffuse sheet-like and clustered pattern of tumor growth with v ariable degrees of vascular differentiation. A tubulopapillary growth pattern, often seen in mesothelioma, was prominent in four cases. Nine cases showed a variable number of spindle cells, some neoplastic, oth ers reactive, focally producing a biphasic growth pattern, further sug gesting mesothelioma. Initial interpretations included mesothelioma, a denocarcinoma, and, in one case with prominent spindle-cell components , leiomyosarcoma. Immunohistochemically, strong vimentin staining and negative or weak to moderate cytokeratin staining were observed in all 14 cases. The tumor cells coexpressed at least two of the four endoth elial markers used in the study (CD31, CD34, von Willebrand factor, an d Ulex europaeus agglutinin-I [UEA-I]). Detection of abortive vessel f ormation was facilitated by staining for collagen type IV. Markers of mesothelial, epithelial, muscular, and neuronal differentiation were a ll negative in the subset of cases studied. As a control group, 39 mes otheliomas and more than 60 adenocarcinomas of various origins were st udied using the same antibody panel. This group revealed strong kerati n staining, moderate or negative vimentin staining, and no expression of any of the endothelial-lineage markers, with the exception of posit ive staining for UEA-I in occasional adenocarcinomas. Clinically, thes e endothelial tumors were highly aggressive; 12 patients presented wit h disseminated disease, and most died within months of the initial pre sentation. These findings indicate that, although uncommon, EHE/EA sho uld be included in the differential diagnosis of serous membrane neopl asms with histological and clinical features of malignant mesothelioma The diagnosis of an endothelial neoplasm can be suspected by the pres ence of abortive vessel formation and by the strong expression of vime ntin, with absent or low-level expression of cytokeratin. The demonstr ation of immunoreactivity for two or more endothelial-associated marke rs is essential in confirming the diagnosis.