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Thyroid Late Effects

Sometimes certain treatments for childhood cancer can affect the thyroid gland.

This damage is usually very easy to treat.

Signs and symptoms may not show up for years after treatment.

Learn More About the Endocrine System

How the Thyroid Gland Works

The thyroid gland is located in the lower part of the neck in front of the trachea, also known as the windpipe.

The gland produces 2 hormones: triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in:

  • Growth
  • Metabolism
  • Energy level
  • Mental development
  • Body temperature

The pituitary gland makes thyroid stimulating hormone (TSH). It releases TSH in response to the levels of T3 and T4 in the blood.

If the levels are low, the pituitary gland makes more TSH to increase the production of thyroid hormones. If T3 and T4 levels are high, the pituitary makes less TSH to signal the thyroid gland to slow down production.

The thyroid gland makes thyroxine, a hormone that plays an important role in growth and mental development. Thyroxine, T4, also helps regulate the body’s temperature and metabolism.

The thyroid gland makes thyroxine, a hormone that plays an important role in growth and mental development. Thyroxine, T4, also helps regulate the body’s temperature and metabolism.

Causes of Thyroid Problems

  1. People who received radiation to areas affecting the thyroid and/or pituitary glands are at risk for thyroid problems. The risk of thyroid problems increases with increasing dose of radiation.

    These areas include:

    • Head/brain
    • Neck
    • Total body
  2. Other treatments that may affect thyroid function include:

    • Surgical removal of the thyroid gland (thyroidectomy)
    • Radioiodine treatments (I-131 thyroid ablation)
    • High doses of MIBG (sometimes used in the treatment of neuroblastoma)
  3. Other factors may include being:

    • Female
    • Treated at a young age

    Thyroid problems may occur soon after radiation but generally do not occur until several years later.

What Problems Can Occur

Problems that may occur:

  • Hypothyroidism – An underactive thyroid
  • Hyperthyroidism – An overactive thyroid
  • Thyroid nodules – Benign growths on the thyroid
  • Thyroid cancer – Malignant growths on the thyroid
  1. Hypothyroidism is the most common thyroid problem in childhood cancer survivors.

    It occurs when the thyroid is not active enough. Thyroid hormone levels are low and body’s metabolism slows down.

    Three types of hypothyroidism occur in childhood cancer survivors:

    • Primary hypothyroidism is caused by direct damage to or surgical removal of the thyroid gland. Blood tests in people with primary hypothyroidism show a high TSH level. The pituitary gland is responding to the lower than normal levels of T3 and T4.
    • Central hypothyroidism occurs because of damage to the hypothalamus or pituitary gland. Blood tests in people with central hypothyroidism show low TSH, T3, and T4 levels. The pituitary gland does not produce enough TSH to stimulate secretion of T3 and T4.
    • Compensated hypothyroidism occurs when the pituitary gland has to overwork the thyroid gland to keep the level of thyroid hormones normal. This may either be a temporary problem after radiation or a sign that the thyroid gland is starting to fail. Blood tests show higher than normal TSH levels and normal T3 and T4 levels.

    Signs and symptoms of hypothyroidism

    • Feeling tired and listless
    • Hoarse voice
    • Problems concentrating
    • Feeling sad/ depressed
    • Mood changes
    • Constipation
    • Weakness
    • Feeling cold all the time
    • Puffiness around the eyes
    • Slowing of normal growth
    • Delayed onset of puberty
    • Puffiness of the face and hands
    • Weight gain
    • Dry skin
    • Brittle hair
    • Muscle and joint aches
    • Slowing of the heart rate
    • Low blood pressure
    • High cholesterol level
    • Poor exercise tolerance

    Treatment for Hypothyroidism

    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.

  2. Symptoms of hyperthyroidism may include:

    • Nervousness or irritability
    • Fatigue or muscle weakness
    • Trouble tolerating heat
    • Trouble sleeping
    • Shaky hands
    • Rapid and irregular heartbeat
    • Frequent bowel movements or diarrhea
    • Weight loss
    • Mood swings
    • Goiter

    Hyperthyroidism may be treated with:

    • Medication on a temporary basis to prevent thyroid hormone production
    • Thyroid ablation — This treatment involves drinking a radioactive liquid iodine called (I-131) to destroy hormone-producing cells.
    • Surgery to remove the thyroid gland

    Treatment for hyperthyroidism may result in hypothyroidism. It is then treated with a daily thyroid pill.

  3. Thyroid Nodules

    Thyroid nodules need additional testing. These tests may include ultrasound and biopsy. If nodules are enlarging, the patient may have surgery to remove them because of concern about thyroid cancer.

    Thyroid Cancer

    Treatment involves surgery. The surgeon may remove a part of the thyroid or the whole thyroid in addition to affected lymph nodes in the neck. Treatment with radioactive iodine (I-131) may be necessary to destroy remaining thyroid tissue. After treatment, most people will need to take daily thyroid hormone replacement pills.

What Survivors Can Do

Know Your Risks and Monitor Your Health

Ask your oncologist about your risks of developing late effects.

Inform your primary health care provider about your risks. Share a copy of your Survivorship Care Plan, which includes a treatment summary. The summary includes details about your cancer treatment and information about health problems that may occur because of treatment.

Regular check-ups

Survivors should have yearly check-ups with a health care provider.

The check-up should include evaluation of growth in children and teens, examination of the thyroid gland, and a blood test to measure the levels of TSH and T4.

During periods of rapid growth, health care providers may recommend more frequent monitoring of thyroid levels.

If problems with thyroid levels are identified, health care providers may refer survivors to an endocrinologist. If a lump is detected on the thyroid, survivors may be referred to a surgeon or other specialist.

Pregnancy-related concerns

Female survivors at risk for thyroid problems who are planning to become pregnant should have their thyroid function checked before attempting pregnancy.

Expectant 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.

Reviewed: November 2019