Angiomatoid carcinoma of the thyroid gland. Anaplastic carcinoma with follicular and medullary features mimicking angiosarcoma.

A 79-year-old man with a 28-year history of a substernal goiter had an anaplastic thyroid neoplasm with prominent angiomatoid features develop. Based on the light microscopic appearance of the tumor and the presence of immunocytochemical staining for Factor VIII-related antigen, a diagnosis of angiosarcoma was made. Subsequent immunocytochemical and ultrastructural studies suggested follicular and medullary differentiation without staining for Ulex europeaus I lectin or evidence of Weibel-Palade bodies. Based on these findings, the tumor is interpreted as an anaplastic carcinoma with evidence of mixed follicular and medullary differentiation and extensive intravascular growth producing an angiomatoid appearance. Positivity for Factor VII-related antigen may be due to nonspecific uptake of antigen-rich serum and platelets by the phagocytic tumor cells. Factor VIII-related antigen immunoreactivity should be interpreted with caution in intravascular neoplasms.