Localization of carcinoembryonic antigen in medullary thyroid carcinoma by immunofluorescent techniques.

Cellular localization of carcinoembryonic antigen (CEA) in medullary thyroid carcinoma was studied in ethanol-fixed, paraffin-embedded specimens using the direct and indirect immunofluorescent techniques. It was demonstrated that CEA was present not only on the surface, but also in the cytoplasm of tumour cells. The immunofluorescence in the cytoplasm differed considerably in intensity from cell to cell. By contrast, no significant fluorescence was demonstrated in tissues of other types of thyroid adenocarcinoma, adenoma. Graves' disease and normal thyroid, with few exceptions. The results obtained indicate that CEA is actively produced by the tumour cells, and is present as a constituent of the cell membrane.