Immunohistochemical reclassification of anaplastic carcinoma reveals small and giant cell lymphoma.

Thirty-one cases of thyroid malignancies which were originally classified as anaplastic carcinoma were reexamined immunohistochemically using PAP methods (peroxidase:antiperoxidase) for IgM, IgG, IgA, cytokeratin, calcitonin, lysozyme and alpha-1-antitrypsin. The reclassification results were compared with patient data such as clinical symptoms, treatment modalities, and clinical outcome. Postoperative radiotherapy was carried out in more than 80% of cases, chemotherapy in none. Seven of 31 tumors showed a positive staining for IgM (n = 4), IgG (n = 2), and IgA (n = 1) antibodies. All of these cases were negative for epithelial markers. Surprisingly, not only all small cell tumors (n = 3) but also 4 tissues with predominantly giant cell areas were among those reclassified as primary malignant lymphoma.