Carcinoembryonic antigen in medullary thyroid carcinoma: an immunohistochemical study applying six novel monoclonal antibodies.

Six novel mouse monoclonal antibodies raised against carcinoembryonic antigen (CEA) were used to study 22 medullary, ten papillary, ten follicular, and eight anaplastic thyroid carcinomas. The antibodies CEA 12-140-5, -7, and -10 reacted with the same epitope group (GOLD 4), whereas antibodies CEA 12-140-1, -2, and -4 recognized different epitopes (GOLD 5, 2 and 1, respectively) on the CEA molecule. All medullary carcinomas of the thyroid (MCTs) were stained when the antibodies CEA 12-140-5, -7, and -10 were applied, whereas CEA 12-140-1 stained all but five MCTs; CEA 12-140-2 and CEA-12-140 -4 each stained all but two. The CEA immunoreactivity was predominantly located diffusely in the cytoplasm but occasionally was also concentrated along the cell membrane. CEA immunoreactivity was also observed in normal C-cells and C-cell nodules. The follicular, papillary, and anaplastic carcinomas were all CEA-negative with the monoclonal antibodies applied in this study. The differences in staining pattern of MCTs found with the various antibodies may be explained as a lack of expression of some epitopes in some tumors, or they may be due to a varying degree of masking of the epitopes by the extensive glycosylation of CEA and CEA-like substances.