Mucinous carcinoma (poorly differentiated carcinoma with extensive extracellular mucin deposition) of the thyroid: a case report with immunohistochemical studies.

We report on a case of mucinous carcinoma of the thyroid in an 82-year-old Japanese woman. The 3 x 2 x 2-cm thyroid tumor located in the patient's right lateral lobe was soft and yellowish gray on the cut section. Microscopically, the tumor was composed entirely of strands or solid clusters accompanied by extensive extracellular mucin. Extracellular mucin was positive with Alcian blue stain and negative with periodic acid-Schiff stain. Immunohistochemically, the tumor cells were positive for thyroglobulin, thyroid-specific transcription factor 1, and low-molecular-weight cytokeratin but negative for carcinoembryonic antigen, calcitonin, and high-molecular-weight cytokeratin. The MIB-1 labeling index was rather high (11%), and immunoexpression of p53 was detectable in the nuclei of carcinoma cells. From these findings, we classified the present tumor as a mucinous carcinoma of the thyroid (poorly differentiated thyroid carcinoma producing massive extracellular mucin). The patient died of multiple metastases 4 years after the initial operation.