Thyroid tumour. Light micrograph of a section through tissue from a Hurthle cell adenoma. This is a rare type of thyroid tumour with a particular type of cell called Hurthle cells. This tumour is often highly malignant, spreading to bones and the lungs. The thyroid gland secretes the hormone thyroxine that controls the body's metabolic rate. Because the normal treatment for thyroid cancers, radioactive iodine, does not work well for this tumour, it is normally surgically removed.