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Some treatments for children's cancer may affect the thyroid gland. These effects are usually very easy to treat. Regular check-ups may help find thyroid problems early so that the proper treatment can be started.
The thyroid gland is located in the lower part of the neck in front of the windpipe. The gland makes two hormones, thyroxine (T4) and triiodothyronine (T3) that play an important role in growth and mental development, and help to regulate the body's metabolism. The thyroid gland is controlled by the pituitary, a gland in the brain that makes thyroid stimulating hormone (TSH). TSH is released from the pituitary in response to the levels of T4 and T3 in the blood. If the levels are low, the pituitary makes more TSH to signal the thyroid to increase the production of thyroid hormones. If T4 and T3 are high, the pituitary makes less TSH to signal the thyroid gland to slow down production.
Damage to the thyroid gland after children's cancer is usually the result of radiation to the brain or neck and may not show up for years after treatment. Several different types of thyroid problems may develop including an underactive thyroid (hypothyroidism), overactive thyroid (hyperthyroidism), and growths on the thyroid that may be benign (nodules) or malignant (cancer).
Hypothyroidism occurs when the thyroid gland is not active enough. This is the most common thyroid problem seen in children's cancer survivors. When the thyroid gland is underactive, thyroid hormone levels are low and the body's metabolism slows down.
There are three different types of hypothyroidism seen in children's cancer survivors:
Primary hypothyroidism is caused by direct damage to the thyroid gland. Blood tests in people with primary hypothyroidism show a high TSH because the pituitary gland is responding to the lower-than-normal levels of T3 and T4 produced by the damaged thyroid gland.
Central hypothyroidism is caused by damage to the pituitary gland in the brain. Blood tests in people with central hypothyroidism show low TSH, T3 and T4 levels because the pituitary gland does not produce enough TSH to signal the thyroid gland to keep the proper levels of T3 and T4 in the blood.
Compensated hypothyroidism occurs when the pituitary gland has to overwork the thyroid gland to keep the level of thyroid hormones normal in the blood. This may be a temporary problem after radiation, or it may be a sign that the thyroid gland is beginning to fail. Blood tests in people with compensated hypothyroidism show higher-than-normal TSH levels and normal T3 and T4 levels. Some survivors with compensated hypothyroidism may be treated with thyroid hormone in order to decrease the workload on the thyroid gland.
Occurs when the thyroid gland is too active. In this condition thyroid hormone levels are high and the body's metabolism speeds up.
Thyroid nodules and cancer are growths that may occur many years after radiation to the thyroid gland. Both usually begin as slow-growing, painless lumps in the neck. Most thyroid growths do not usually cause any symptoms.
People who received radiation that may have affected the thyroid gland directly are at risk for primary hypothyroidism, compensated hypothyroidism, hyperthyroidism, thyroid nodules, and/or thyroid cancer. The following radiation fields have the potential to affect the thyroid gland directly:
People who received radiation that may have affected the pituitary gland in the brain are at risk for central hypothyroidism. The following radiation fields have the potential to affect the pituitary gland:
Other factors that have been shown to increase the risk of thyroid problems after children's cancer include being:
Thyroid problems may occur soon after radiation, but generally do not occur until several years later. If treated promptly, thyroid problems are easily managed.
Since thyroid problems may occur many years after cancer treatment, a yearly check-up is recommended for survivors who are at risk of developing thyroid problems. This check-up should include evaluation of growth in children and teens, palpation (feeling) of the thyroid gland, and a blood test to measure the levels of TSH and T4. During periods of rapid growth, healthcare providers may recommend more frequent monitoring of thyroid levels.
Female survivors at risk for thyroid problems who are planning to become pregnant should have their thyroid levels checked before attempting pregnancy. It is important to do this before becoming pregnant, because mothers with thyroid disease have a higher chance of having babies with developmental problems. It is also important to monitor thyroid levels periodically during pregnancy.
If problems with thyroid levels are identified, you may be referred to an endocrinologist (hormone specialist) for continuing treatment. If a lump is detected on the thyroid, you may be referred to a surgeon or other specialist for evaluation and management. All types of hypothyroidism are treated with daily thyroid pills. Treatment is usually for life. In some cases of compensated hypothyroidism, treatment may be stopped if the thyroid gland begins to work normally.
Hyperthyroidism may be treated in several ways. Sometimes medication is given on a temporary basis to prevent thyroid hormone production. Thyroid ablation (destroying the hormone-producing cells in the gland by drinking a radioactiveliquid iodine called I-131) may be done. Surgery to remove the thyroid gland is another treatment. Your healthcare provider will determine which treatment option is the best choice for you. Treatment for hyperthyroidism may result in hypothyroidism, which is then treated with a daily thyroid pill.
Thyroid nodules that are felt on physical exam need additional testing. This is generally done with an ultrasound (picture made using sound waves) and biopsy (sampling the thyroid tissue to check for cancer cells). Surgery may be done to remove enlarging nodules because of the concern about thyroid cancer. Treatment for thyroid cancer involves surgery to remove the cancer and as much additional normal thyroid tissue as the surgeon feels is necessary. After surgery, additional treatment with radioactive iodine (I-131) may be needed to destroy any remaining thyroid tissue. After treatment for thyroid cancer, most individuals will need to take daily thyroid pills.