When thyroid carcinoma is recurrent or metastatic and is also widespread or can't be removed, it is treated with radioactive iodine. If it does not take up radioactive iodine, it should be treated with radiation therapy .
• For the papillary and follicular types, an effort is made to scan for metastatic disease with radioactive iodine.
  After the thyroid gland is removed and thyroid hormone is stopped for an appropriate time, a tracer dose of
  radioactive iodine is given. If hot spots appear at sites outside the thyroid area, suggesting metastases, a
  therapeutic dose of radioactive iodine is given. Radioactive iodine effectively irradiates microscopic
   metastases. Larger metastases should be removed surgically before radioactive iodine is given. The
  thyroglobulin level should be determined, since if it is detectable or elevated after a total thyroidectomy,
  residual tumor is present.
• External radiation is used in patients whose tumors do not take up radioactive iodine or are undifferentiated .
• Some patients respond to chemotherapy , with regimens containing doxorubicin having the highest response
  rate. The combination of cisplatin and doxorubicin may produce some complete and partial remissions in
  metastatic thyroid cancer. In a few cases, the complete responders survived more than two years. Another
  combination (doxorubicin + bleomycin + vincristine + melphalan) was reported to show responses in about
  one-third of patients.
• In patients with anaplastic thyroid cancer, chemotherapy is occasionally effective and is usually combined
  with external radiation.