Residual normal gland containing colloid (left) is seen among nests of highly pleomorphic hyperchromatic cells.
Areas of squamoid differentation consisting of epithelioid cells with increased cytoplasm are seen.
Some squamoid areas are reminiscent of keratin pearls (center).
Undifferentiated (anaplastic) carcinomas of the thyroid usually affect the elderly and present as firm fixed masses. It is thought the the tumor arises from dedifferentiation of a pre-existing well-differentiated papillary carcinoma, however, there are a subset of tumors that arise de novo.
Histologically, the tumor is composed of spindle cells, pleomorphic giant cells and epithelioid cells. One cell type may predominate. In this case, the tumor was composed of predominantly of pleomorphic epithelioid cells with areas of squamoid differentiation.
The prognosis is dismal and most survive only 6 months.
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