Immunostaining for Leu-7 in the diagnosis of thyroid carcinoma

The morphologic distinction between benign and malignant thyroid lesions can be difficult. Immunostaining for the Leu-7 antigen has been reported to be useful in the diagnosis of thyroid carcinoma. To test the specificity of immunostaining for Leu-7 in the diagnosis of thyroid carcinoma, we studied formalin-fixed, paraffin-embedded tissue specimens obtained from 66 thyroid lesions using the HNK-1 monoclonal antibody to Leu-7 and an avidin-biotin-complex technique. Positive reactivity for Leu-7 was seen in 11 (33%) of 33 benign thyroid conditions and in 27 (82%) of 33 thyroid carcinomas. We conclude that immunostaining for Leu-7 is not specific in the diagnosis of thyroid carcinoma.