Hürthle cell medullary carcinomas of the thyroid gland

Two medullary carcinomas of the thyroid (MCTs) composed entirely of Hürthle (oncocytic or oxyphilic) cells and containing follicular structures are described. Immunocytochemical analysis showed these tumours to be calcitonin-, carcino-embryonic antigen- and neuron-specific enolase-positive. The essence of this communication is twofold. Firstly, it highlights and draws attention to this unusual variant of MCT, which may be encountered at frozen section and misdiagnosed as a Hürthle cell tumour of follicular cell origin. Secondly, it undertakes a concise overview of the immunocytochemistry of Hürthle cell thyroid neoplasms and MCT.