Angiosarcoma-like neoplasms of epithelial organs: true endothelial tumors or variants of carcinoma?

Past experience has shown the existence of tumors in various viscera that assume growth patterns that are usually associated with angiosarcomas of skin and soft tissue. The lineage of differentiation pursued by the former of these proliferations has been the subject of controversy, with some investigators concluding that "angiosarcomatoid" neoplasms of solid organs were, in actuality, variants of high-grade carcinomas. The latter statement does appear to have partial validity, inasmuch as immunohistologic, ultrastructural, and clinical data on "pseudovascular carcinomas" do support their basic identity with high-grade epithelial malignancies of the breasts, skin, and lungs. Those lesions show uniform reactivity for keratin and epithelial membrane antigen, but they fail to express von Willebrand factor, CD31, or CD34, which are regarded as endothelial determinants. On the other hand, however, angiomatoid neoplasms of the thyroid gland are more complex; some represent indisputable carcinomas, others manifest seemingly "pure" mesenchymal phenotypes, and still others display a mixture of epithelial and endothelial phenotypes at ultrastructural and protein-chemical levels of specialized investigation. At present, it must be acknowledged that the distinction between angiomatoid thyroid carcinomas and "true" thyroid angiosarcomas is an academic one, because the prognoses and treatments for these lesions are essentially identical.