Mucus-producing medullary cell carcinoma of the thyroid gland.

A case of medullary carcinoma of the thyroid with the presence of mucus-secreting (goblet) cells was reported. Ultrastructurally, the tumor was composed of two types of cells, one with neurosecretory granules and the other with mucus granules. The secretion of calcitonin and mucus was demonstrated by histochemical methods. The presence of two cell populations in this tumor casts doubts on the "APUD" concept, which proposes a neuroectodermal origin for parafollicular (C) cells of the thyroid gland. The significance of this tumor with regard to the histogenesis of the cells involved, is discussed.