Immunohistochemical demonstration of thyroid peroxidase (TPO) in human thyroid tissues from various thyroid diseases.

Human thyroid peroxidase (hTPO) was detected immunohistochemically in 61 normal, benign and malignant thyroid tissues with a monoclonal antibody (38E) against hTPO using paraffin-embedded sections. Thyroid peroxidase was expressed intensely not only in tissues from Graves disease and hyperfunctioning adenomas, but also in those from carcinomas, adenomas and Hashimoto's thyroiditis. The staining pattern of TPO in the follicular cells was a diffuse and fine granular one in the normal thyroids, Graves' thyroids and adenomas, but abnormal coarse granular deposits of TPO were characteristically identified in most of the papillary carcinomas and Hashimoto's thyroiditis. These coarse granular deposits of TPO suggested that qualitative or structural changes in the TPO molecule are present in carcinomas and Hashimoto's thyroiditis. Consequently, these qualitative changes in TPO may be responsible for the lack of biochemically measured TPO activity in these diseases. This finding may also be useful in distinguishing between benign and malignant thyroid tumors.