The cause is unknown, but is not thought to be related to radiation therapy, as opposed to other thyroid cancers. Thyroid function tests are usually normal. Risk factors are a family history of multiple endocrine neoplasia (MEN), a prior history of pheochromocytoma, mucosal neuromas, or hyperparathyroidism.

The average age at diagnosis is the mid-40s, except in patients with inherited cancer syndromes, in which the cancer often occurs earlier. Other types of thyroid cancer are papillary carcinoma of the thyroid, anaplastic carcinoma of the thyroid, follicular tumor of the thyroid, thyroid lymphoma, and metastatic thyroid cancer. Approximately 700 new cases are diagnosed each year in the United States.