Aspiration cytology of the osteoclastic variant of anaplastic thyroid carcinoma: With special emphasis on the undifferentiated mononuclear cells

Anaplastic thyroid carcinoma (ATC) is an uncommon aggressive malignant tumor, and the osteoclastic variant of ATC is extremely rare. We report here on the fine needle aspiration cytology of the osteoclastic variant of ATC in an 83-year-old woman. The smear was composed of many oval to slightly elongated undifferentiated mononuclear cells admixed with multinucleated osteoclast-like giant cells. The mononuclear tumor cells revealed inconspicuous nuclear pleomorphism and the nuclei were characterized by vesicular chromatin and an indented or lobulated nuclear membrane with conspicuous nuclear grooves. A few epithelial clusters suggestive of a papillary carcinoma component were also observed. Making the proper cytological diagnosis of the osteoclastic variant of ATC is helpful to determine the proper treatment modality for these patients.