Exposure to I-131 may increase a person's risk of developing thyroid cancer. It is thought that risk is higher for people who have had multiple exposures and for people exposed at a younger age. Thyroid cancer accounts for less than 2 percent of all cancers diagnosed in the United States. Typically, it is a slow-growing cancer that is highly treatable and usually curable. About 95 out of 100 people who are diagnosed with thyroid cancer survive the disease for at least five years, and about 92 out of 100 people survive the disease for at least 20 years after diagnosis.

The cause of most cases of thyroid cancer is not known. Exposure to I-131 can increase the risk of thyroid cancer. But even among people who have documented exposures to I-131, few develop this cancer. It is known that children have a higher-than-average risk of developing thyroid cancer many years later if they were exposed to radiation. This knowledge comes from studies of people exposed to x-ray treatments for childhood cancer or noncancerous head and neck conditions, or as a result of direct radiation from the atomic bombings of Hiroshima and Nagasaki.

The thyroid gland in adults, however, appears to be more resistant to the effects of radiation. There appears to be little risk of developing thyroid cancer from exposure to I-131 or other radiation sources as an adult.

There is no single or specific symptom of thyroid cancer. Doctors screen for thyroid cancer by feeling the gland, to check for a lump or nodule. If a doctor feels a nodule, it does not mean cancer is present. Most thyroid nodules found during a medical exam are not cancer.

If thyroid cancer is found, it is treated by removing the thyroid gland. People who undergo surgery will need to take thyroid hormone replacement pills for the rest of their lives. Although this is inconvenient and expensive, cancer survival rates are excellent. In fact, the cause of death among people who once had thyroid cancer is rarely the result of the return or spread of the same cancer.

Living with a serious disease like thyroid cancer isn't easy. A cancer diagnosis can be devastating. Some people find they need help coping with the emotional and practical aspects of their disease. Doctors and other health professionals can help with concerns about treatment and managing side effects. Support groups can help also. The National Cancer Institute's Cancer Information Service can help put you in touch with support groups in your community. Call 1-800-4-CANCER for more information.

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