Some patients who have been diagnosed with metastatic thyroid cancer that has spread to other parts of the body may develop hyperthyroidism related to the continuing growth of thyroid cancer cells. If these thyroid cancer cells retain the ability to produce thyroid hormone, they may escape from the normal control exerted by the pituitary gland, producing and secreting excess amounts of thyroid hormone.
In very rare cases, patients with normally functioning thyroid glands may present with hyperthyroidism caused by the production and secretion of excess amounts of TSH from a tumor that develops in the pituitary gland. This type of tumor is called a TSH-secreting pituitary adenoma.
Women who are diagnosed with a type of ovarian tumor called a teratoma may develop hyperthyroidism if portions of the tumor grow to form thyroid tissue. This thyroid tissue may produce and secrete thyroid hormone in an uncontrolled manner, or it may trigger an autoimmune response that stimulates the thyroid gland to produce and secrete excess amounts of thyroid hormone. This extremely rare disorder is called struma ovarii.