Mixed follicular and parafollicular thyroid carcinoma

A rare case of mixed follicular-parafollicular thyroid carcinoma which occu rred in a 50-year-old man, is reported. The ultrastructural aspects of the tumor showed: a biphasic growth pattern with microfolliculi and solid areas ; the coexpression of thyroglobulin and calcitonin antigens in the same fol licle-like structures; the presence of neuroendocrine granules, microvilli and intracytoplasmic canaliculi bordered by microvilli. These characteristi cs lead us to a diagnosis of mixed follicular-parafullicolar thyroid carcin oma.