MIXED MEDULLARY-FOLLICULAR CARCINOMA OF THE THYROID-GLAND - A CLINICOPATHOLOGICAL VARIANT OF MEDULLARY-THYROID CARCINOMA

A rare case of mixed medullary-follicular carcinoma of the thyroid gla nd, which occurred in a 44-year-old man, is reported. The thyroid tumo r was composed of solid nests of polygonal cells, with an admixture of many evenly distributed thyroid follicles that contained colloid. The lymph node metastases were the same composition as the primary, with follicle formations that contained colloid. Immunohistochemically, in both the primary and metastatic lesions, calcitonin and carcinoembryon ic antigen were present in the predominant solid areas of medullary ca rcinoma, whereas thyroglobulin was demonstrated in the follicular stru ctures. At the ultrastructural level, most of the tumor cells containe d numerous neurosecretory granules, but some showed follicular cell di fferentiation. These findings fulfilled the criteria of mixed medullar y-follicular carcinoma of the thyroid according to the World Health Or ganization classification and also suggested dual neuroendocrine and f ollicular differentiation of this type of thyroid carcinoma. We review ed the literature on mixed medullary-follicular carcinoma of the thyro id and concluded that it might constitute another clinicopathologic en tity different from conventional medullary thyroid carcinoma; it occur s predominantly in younger males and is associated with a more favorab le clinical course than the usual medullary thyroid carcinoma.