This report presents a very rate histologic variation of medullary carcinoma of the thyroid, referred to as squamous variant, which is similar to squamous cell carcinoma arising in other organs. However, squamous variant of medullary thyroid
carcinoma
shows C cell differentiation as well as squamous differentiation of tumor cells which is shown in primary squamous cell carcinoma of the thyroid. A lot of histologic variation of medullary thyroid carcinoma have been reported. Thus, it is
difficult
to
diagnose medullary carcinoma accurately by conventional histologic examination, so special examinations such as immunohistochemical stains and electron microscopy are required.
We report a case of squamous variant of medullary carcinoma involving right lobe of the thyroid. The patient was a 62 year-old female with complaints of horseness for 2 months. On neck computerized tomography(CT), an irregular solid mass of right
lobe
displacing trachea to the left, 4 cm in the largest diameter, was found. Total thyroidectomy was done.
Grossly, an ill-defined mass was homogenously whitish solid. No hemorrhage and necroses were found. Microscopically, irregular tumor nests within fibrotic stroma were composed of polygonal cells with peripheral squamous differentiation. Also,
amorphous
eosinophilic deposits within stroma were found.
Special stain for amyloid(congo-red) showed apple green birefringence within stroma and tumor nests under polarizing microscope. Immunohistochemical stains for carcinoembryonic antigen(CEA), calcitonin, cytokeratin(broad spectrum and CAM 5.2),
synaptophysin, and chromogranin showed positive reaction in tumor cells, but thyroglobulin revealed negative reaction, and neuron-specific enolase(NSE0 was focally weak-positive.
Ultrastructurally, the tumor was mainly composed of two types of cell. One type showing squamous differentiation had numerous tonofilaments and desmosomes in the cytoplasm.
Another type of cells showed a few electron-dense core granules, about 200nm, and abundant RER which were considered as tumor cells showing C-cell differentiation. The stroma showed abundant collagen fibrils. Some of the cells showing hybrid
composed of
squamous and C-cell differentiation were observed.
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