Lymphoepithelioma-like anaplastic thyroid carcinoma: report of a case not related to Epstein-Barr virus

A 68-year-old man developed a rapidly growing thyroid tumor that extended into the retropharyngeal, prevertebral, and perilaryngeal spaces, and eventually invaded the esophagus. The patient was treated with radiotherapy, obtaining a good but incomplete response. The neoplasia was composed of sinctitial sheaths of epithelial cells with large vesicular nuclei, prominent nucleoli, and high mitotic activity. There was abundant lymphoid infiltrate surrounding and invading the cell sheaths. The overall picture was of a lymphoepithelioma, but no evidence of Epstein-Barr virus infection was detected by studies of immunohistochemistry and polymerase chain reaction. We believe this case represents a morphologic variant of anaplastic carcinoma that should be separated from carcinoma showing thymus-like differentiation, a tumor that also resembles lymphoepithelioma but has an indolent course. Ann Diagn Pathol 5:21-24, 2001.