Difficulties of differential diagnosis between epitheliod angosarcoma and anaplastic carcinoma in thyroid gland In this study, a case of a malignant thyroid tumor in a 60 years old male man presented. The tumor showed morphological and immunohistochemical evidence of endothelial differantiation Strong immunoreactivity for both Q BEND/10 and high molecular weight keratin (AE3) in neoplastic cells with epitheloid apperance have been detected. Primary angiosarcoma of the thyroid is a controversial subject. Some authors contend that most of these tumors were anaplastic carcinomas. In our case, the findings support a diagnosis of epithelioid angiosarcoma.