An immunohistochemical study of thyroid Hurthle cells and their neoplasms: the roles of S-100 and HMB-45 proteins.

The histological and cytological features of follicular thyroid neoplasms with oxyphilic change (Hurthle cell tumors) may lead to the differential diagnosis of metastatic malignant melanoma. S-100 and HMB-45 staining was studied in 18 Hurthle cell tumors, 6 Hurthle cell carcinomas, and 5 cases of Hashimoto's thyroiditis using a rabbit polyclonal antibody to S-100 protein, a mouse monoclonal antibody to HMB-45 protein, and the avidin alkaline phosphatase method. All 6 carcinomas and 17 of 18 Hurthle cell tumors exhibited strong cytoplasmic and nuclear staining for S-100. One Hurthle cell carcinoma also contained a spindle cell anaplastic area that was negative for S-100. All cases of Hashimoto's thyroiditis displayed intense staining in Hurthle cells for S-100, with weak to negative staining in nonoxyphilic follicular epithelium. In the three studied lesions, all cases were negative for HMB-45 protein. Three nonthyroid oncocytic tumors (renal oncocytoma, oncocytic carcinoma of the parotid, and parathyroid oxyphilic adenoma) were found to be negative for both S-100 and HMB-45 staining. Hurthle cell lesions should be included in the differential diagnosis of S-100-positive tumors. HMB-45 remains a marker more restricted to melanocytic lesions.