Thyroid often carcinomas, although cancer can occur in any tissue that the thyroid consists of, including cancer of C-cells and lymphomas. Cancers from other sites also rarely lodge in the thyroid. Radiation of the head and neck presents a risk factor for thyroid cancer, and cancer is more common in women than men, occurring at a rate of about 2:1. In most cases, thyroid cancer presents as a painless mass in the neck. It is very unusual for thyroid cancers to present with other symptoms, although in some cases cancer may cause hyperthyroidism. Most malignant thyroid cancers are papillary, followed by
Thyroid peroxidase Thyroid peroxidase Thyroid peroxidase, also called thyroperoxidase (TPO) or iodide peroxidase, is an enzyme expressed mainly in the thyroid where it is secreted into colloid. Thyroid peroxidase oxidizes iodide ions to form iodine atoms for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T) or triiodothyronine (T), the thyroid hormones. In humans, thyroperoxidase is encoded by the "TPO" gene. + I + H+ HO ⇒ + 2 HO Iodide is oxidized to iodine radical which immediately reacts with tyrosine. The second iodine atom is added in similar manner to the reaction intermediate 3-iodotyrosine. Inorganic iodine enters the