TPO (Thyroid Peroxidase) is an enzyme expressed in the thyroid gland. Thyroid peroxidase oxidizes iodine ions to form iodine atoms, which bind to the tyrosine residues of thyroglobulin to produce thyroxine T4 and three-point thyroxine T3.
It is mainly used to detect the expression level in thyroid cancer and distinguish normal thyroid from benign and malignant thyroid tumors.