Malignant vascular tumors of the serous membranes mimicking mesothelioma. A report of 14 cases.

Malignant endothelial neoplasms involving the serous membranes are rare, and only a few cases have been documented. We report 14 patients with epithelioid hemangioendothelioma (EHE) or epithelioid angiosarcoma (EA) diffusely involving the pleural, peritoneal, or pericardial cavities, resulting in a picture closely resembling mesothelioma. The mean age at diagnosis was 52 (range, 34-85). The patients included two women and one man with peritoneal tumors, eight men with pleural tumors, and three men with pericardial tumors. A shared histological appearance was a diffuse sheet-like and clustered pattern of tumor growth with variable 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, others reactive, focally producing a biphasic growth pattern, further suggesting mesothelioma. Initial interpretations included mesothelioma, adenocarcinoma, 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 endothelial markers used in the study (CD31, CD34, von Willebrand factor, and Ulex europaeus agglutinin-I [UEA-I)]. Detection of abortive vessel formation was facilitated by staining for collagen type IV. Markers of mesothelial, epithelial, muscular, and neuronal differentiation were all negative in the subset of cases studied. As a control group, 39 mesotheliomas and more than 60 adenocarcinomas of various origins were studied using the same antibody panel. This group revealed strong keratin staining, moderate or negative vimentin staining, and no expression of any of the endothelial-lineage markers, with the exception of positive staining for UEA-I in occasional adenocarcinomas. Clinically, these endothelial tumors were highly aggressive; 12 patients presented with disseminated disease, and most died within months of the initial presentation. These findings indicate that, although uncommon, EHE/EA should be included in the differential diagnosis of serous membrane neoplasms with histological and clinical features of malignant mesothelioma. The diagnosis of an endothelial neoplasm can be suspected by the presence of abortive vessel formation and by the strong expression of vimentin, with absent or low-level expression of cytokeratin. The demonstration of immunoreactivity for two or more endothelial-associated markers is essential in confirming the diagnosis.