A mucinous carcinoma of the thyroid.

A primary mucinous carcinoma of the thyroid is reported. The tumour cells, arranged in small nests and trabecules, were surrounded by abundant intercellular substance which was positively stained for mucicarmine, alcian blue and PAS before and after diastase treatment. Diastase-resistant, PAS-positive material was also present in the tumour cells. Electron microscopy revealed neoplastic cells linked by desmosomes and not surrounded by basal lamina; the nuclei had irregular contours, prominent nucleoli and numerous pseudoinclusions; mucin granules and rough endoplasmic reticulum were the prominent organelles in the cytoplasm. Follicles and follicle-like structures were not found, either by light or by electron microscopy. A definite diagnosis could only be established after the disclosure of intense immunostaining for thyroglobulin in several groups of tumour cells. Criteria for the diagnosis are discussed and the question of histogenesis raised.