Immunostaining for P-glycoprotein in the diagnosis of thyroid carcinomas.

The morphologic distinction between thyroid carcinoma and certain benign thyroid conditions can be difficult in selected cases. P-glycoprotein (Pgp), a glycoprotein associated with tumor multidrug resistance, has been reported to be expressed in thyroid carcinoma but not in benign thyroid conditions. To determine the specificity of immunostaining for Pgp in the diagnosis of thyroid carcinoma, we studied formalin-fixed, paraffin-embedded tissue from 69 cases of various thyroid lesions using a commercially available monoclonal antibody to Pgp (C219, Centocor, Malvern, PA) and an avidin-biotin-peroxidase complex technique. Positive reactivity was seen in 15 of 37 (41%) benign thyroid conditions and in 23 of 32 (72%) thyroid carcinomas. We conclude that immunostaining for Pgp is not specific in the diagnosis of thyroid carcinoma.