Anaplastic type of medullary thyroid carcinoma. An ultrastructural and immunohistochemical study

A case of anaplastic type of medullary thyroid carcinoma is presented. Immunoperoxidase study revealed calcitonin within the tumor cells, which also showed argyrophilia. At ultrastructural examination the tumor also displayed mucoid and squamous differentiation. This multidirectional differentiation (endocrine and exocrine) underlies the difficulty of ascribing a precise histogenesis to this tumor.