ihcDirect® Thyroid Peroxidase (TPO) Ab is a polymerized horseradish peroxidase (pHRP) conjugated mouse monoclonal antibody (clone C129). TPO is a thyroid-specific enzyme involved in thyroid hormone synthesis and its gene expression is regulated by thyroid stimulating hormone. TPO is located in normal thyroid and thyroid carcinoma of papillary and follicular type. In normal thyroid tissue, expression of TPO may produce a diffuse, fine, granular cytoplasmic stain in follicular cells. TPO may aid pathologists to better differentiate benign from malignant thyroid neoplasms and may be useful with other thyroid biomarkers such as; TROP2, Galectin-3, CD56 and CK19.