Medullary thyroid carcinoma with thyroglobulin immunoreactivity. A special entity?

Fourteen medullary carcinomas of the thyroid (MCT) immunoreactive for both thyroglobulin and calcitonin were studied by light microscopy and immunohistochemistry. Thyroglobulin immunoreactivity was seen in neoplastic follicles and/or in solid foci in the lymph node metastases of two cases. Colocalization of thyroglobulin and calcitonin was found in the same neoplastic cells of eight cases using a double immunostaining method; in three of these (including one with metastases), thyroglobulin was found to be colocalized with calcitonin gene related peptide as well. Our histological and immunohistochemical results support the assumption that MCT with thyroglobulin immunoreactivity is an unusual variant of the multihormone producing MCT and strengthen the hypothesis that a common stem cell is the origin of these tumors. The available clinical data suggest that thyroglobulin-positive MCT carry a better prognosis than thyroglobulin-negative MCT.