What is the pathology of anaplastic thyroid carcinoma?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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On gross examination, anaplastic thyroid carcinoma is a large and invasive tumor. Areas of focal necrosis and hemorrhage may be present throughout the tumor, giving a highly variable appearance. The tumor often extends through the capsule of the thyroid gland itself. Areas of well-differentiated thyroid carcinoma are often found concomitantly, and anaplastic thyroid carcinoma is believed to arise from a preexisting, well-differentiated thyroid carcinoma.

On microscopic evaluation, squamoid, spindle cell, and giant cell variants are observed. All 3 histologic variants show high mitotic activity, large foci of necrosis, and notable infiltration. Immunohistochemical stains are often positive for low-molecular-weight keratins and occasionally positive for thyroglobulin. Regarding their ultrastructure, the neoplasms have epithelial features (eg, desmosomes, tight junctions) that are helpful for differentiating them from sarcomas. Small cell carcinomas, which usually represent lymphomas, may be confused with anaplastic thyroid carcinoma.

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