Clear cell variant of medullary carcinoma of the thyroid

A previously unreported clear cell variant of medullary thyroid carcinoma is described. This histologic appearance was observed in sections from both the primary thyroid tumor and a vertebral metastasis. This variant merits recognition because it may be confused with a variety of other tumors occurring in the thyroid that contain cells with optically clear cytoplasm. Immunohistochemical and ultrastructural studies can be helpful in establishing the diagnosis of these tumors.