Medullary cancer of the thyroid is a type of cancer affecting the thyroid, a gland located at the base of the throat. This type of cancer can usually be cured by surgery to remove the thyroid gland. However, if the cancer has metastasized (spread from the thyroid to other parts of the body), treatment becomes more challenging. Recently, researchers reported that the use of a radioactive substance, called iodine 131, may hold promise as a safe and effective treatment for prolonging the survival time for persons with metastatic medullary cancer of the thyroid.
When medullary cancer of the thyroid cannot be cured by surgery, treatment goals are primarily to relieve the symptoms of the disease and prolong survival time. External-beam radiation therapy, radiation delivered from a machine outside the body, may be used to control cancer that recurs in a specific area of the body. Some persons may also respond to the use of intravenous chemotherapy drugs. However, researchers have sought ways to treat persons with metastatic medullary cancer more effectively. This led to the consideration of another form of radiation therapy, the introduction of a radioactive substance, called iodine 131, into the body. The radioactive beta and gamma rays produced by iodine 131 can potentially kill the cells with which it comes in contact in the body. A challenge with this approach is to ensure that the iodine 131 is circulated in the body, and that it targets mainly the cancer cells. Many medullary thyroid cancers express a cancer-associated antigen, called an carcinoembryonic antigen. One way to “deliver” the iodine 131 then is to attach it to a monoclonal antibody that will bind specifically to the carcinoembryonic antigen on the cancer cells. Although the entire body is exposed to the radioactive iodine 131, the radioactive rays are directed primarily at the cancer cells containing the carcinoembryonic antigen. However, young blood-producing cells (called stem cells) in the bone marrow are particularly susceptible to damage from this treatment, making a stem cell transplantation necessary to replace the destroyed stem cells and hasten the production of healthy new blood cells.
Researchers at the Garden State Cancer Center treated 12 persons with metastatic medullary thyroid cancer with iodine 131 and an autologous stem cell transplantation. First, stem cells were removed from the blood of each patient and were frozen, to be re-infused into the patient after the radioactive iodine 131 therapy. The patients then received the radioactive iodine 131, which was attached to a monoclonal antibody that would bind specifically to the carcinoembryonic antigen of the cancer cells. After this therapy was complete, the stem cells that were collected previously were infused back into the patient, to replace those cells damaged by the iodine 131. Results showed that 1 patient had a partial response to the treatment that lasted for 1 year; 1 patient had a response of 3 months; and 10 had stabilized disease (no progression or growth of the cancer) for 1 to 16 months. There were no severe side effects with the treatment.
From these findings, the use of iodine 131, attached to a monoclonal antibody, appears to be a safe treatment. The positive responses found here suggest that studies to optimize the effectiveness of this new treatment further are warranted. Persons who have metastatic medullary thyroid cancer may wish to talk with their doctor about the risks and benefits of the radioactive iodine 131 therapy, or of participating in a clinical trial in which other new treatments are being studied. Sources of information on ongoing clinical trials that can be discussed with a doctor include a comprehensive, easy-to-use service provided by the National Cancer Institute (
Journal of Nuclear Medicine, Vol 41, No 1, pp 93-103, 2000)