Evidence of vascular differentiation in anaplastic tumours of the thyroid--an immunohistological study.

Sixteen cases of anaplastic carcinoma (ACA) and 4 cases of malignant haemangioendothelioma (HAE) of the thyroid were studied by light microscopy and immunohistochemistry. Seven cases of ACA and 3 cases of HAE were characterized by coexpression of immunohistological features of epithelial and vascular endothelial cells. Expression of vimentin was common to all tumours investigated. The present study provides evidence that ACA and HAE are partially closely related tumours showing alternating differentiation. This speaks in favour of a common neoplastic cell with the potential for epithelial and vascular endothelial differentiation.