Factor VIII-related antigen in malignant hemangioendothelioma of the thyroid: additional evidence for the endothelial origin of this tumor.

Malignant hemangioendothelioma of the thyroid gland, which most often originates in a hemorrhagic nodule, is a well-known entity in European alpine regions with endemic goiter. In other parts of the world it very rarely has been diagnosed. This tumor may display considerable morphologic variation and often has been interpreted as a variant of undifferentiated carcinoma. In 13 out of 20 thyroid tumors, classified by light microscopy as malignant hemangioendothelioma, Factor VIII-related antigen, a marker for endothelial cells, was demonstrated in neoplastic cells with the help of immunohistochemical technics applied to conventional paraffin sections. In one case, in which material suitable for electron microscopy was available, Weibel-Palade bodies were found in tumor cells. These findings add strong support to the notion of an endothelial origin of this neoplasm.