Malignant hemangioendothelioma of the thyroid and factor VIII-related antigen.

Thirty-six malignant hemangioendotheliomas of the thyroid were examined immunohistochemically using antibody probes to factor VIII-related antigen in order to reevaluate the histogenesis of this neoplasia. The 36 cases were reclassified according to their light microscopic features without prior knowledge of the immunohistochemical results. Three different tumor types were discerned: Group I: classical hemangioendotheliomas (20 cases); Group II: borderline cases between malignant hemangioendotheliomas and anaplastic carcinomas (14 cases) and Group III: anaplastic carcinomas with hemangio-endotheliomatous features (2 cases). Factor VIII-related antigen could be demonstrated in 12 (60%) tumors of group I, 3 (21%) tumors of group II and in neither tumor of group III. Five control cases with the typical histological picture of anaplastic carcinoma of the thyroid were negative for factor VIII-related antigen. The results of our study suggest that at least part of the tumors termed as malignant hemangioendotheliomas are in fact derived from endothelial cells.