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Thyroid Late Effects

Sometimes certain treatments for childhood cancer can cause problems with the function of the thyroid gland.

The Endocrine System

The thyroid gland is part of the body’s endocrine system, a complex network of glands located throughout the body that produce hormones. The endocrine system controls most of the body’s functions such as growth, puberty, energy level, urine production, and stress response.

The thyroid gland is controlled by the pituitary gland. Located in the brain, the pituitary gland is sometimes called “the master gland” because it also controls other glands such as the adrenals, ovaries (in females), and testes (in males).

A graphic of the thyroid gland, in three versions. At the top is the thyroid gland shown on the trachea. On the bottom, there are two views showing the front (with labels for the left lobe, right lobe, and isthmus) and the back (with labels for four parathyroid glands).

How the Thyroid Gland Works

The thyroid gland is located in the lower part of the neck in front of the windpipe. The gland produces a hormone: thyroxine (T4). This hormone play an important role in growth and mental development. It also helps regulate the body’s temperature and metabolism.

The pituitary gland makes thyroid stimulating hormone (TSH). TSH is released from the pituitary in response to the levels of T4 in the blood. If the levels of T4 are low, the pituitary gland makes more TSH to signal the thyroid to increase the production of T4. If T4 levels are high, the pituitary makes less TSH to signal the thyroid gland to slow down production.

What Problems Can Occur

Several different types of thyroid problems may develop including:

  • Hypothyroidism – An underactive thyroid
  • Hyperthyroidism – An overactive thyroid
  • Thyroid nodules – Benign growths on the thyroid
  • Thyroid cancer – Malignant growths on the thyroid
  1. Hypothyroidism occurs when the thyroid is not active enough. This is the most common thyroid problem seen in childhood cancer survivors. When the thyroid gland is underactive, thyroid hormone levels are low and body’s metabolism slows down.

    Two types of hypothyroidism may 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 because the pituitary gland is responding to the lower than normal levels of T4 produced by the damaged thyroid gland.
    • Central hypothyroidism is caused by damage to the hypothalamus or pituitary gland in the brain. Blood tests in people with central hypothyroidism show low T4 levels without elevation of TSH because the pituitary gland does not produce enough.

    Signs and symptoms of hypothyroidism

    Signs and symptoms may include:

    • 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
  2. Hyperthyroidism occurs when the thyroid gland is too active. Thyroid hormone levels are high and the body’s metabolism speeds up.

    Signs and symptoms of hyperthyroidism

    • Jitteriness
    • Anxiety
    • Problems concentrating
    • Feeling tired
    • Muscle weakness
    • Tremors
    • Fast or irregular heartbeat
    • Increased sweating
    • Feeling hot all the time
    • Diarrhea
    • Weight loss
    • Irregular menstrual period
    • Bulging or protruding eyes
    • Neck tenderness and swelling
    • Poor exercise tolerance
  3. Thyroid nodules and thyroid 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 cause symptoms.

What Cancer Treatments/ Conditions Can Cause Thyroid Problems

Damage to the thyroid gland after childhood cancer is usually the result of radiation to the head, brain, or neck. This damage is usually very easy to treat. It may not show up for years after treatment.

Surgical removal of the thyroid gland (thyroidectomy), radioiodine treatments (I-131 thyroid ablation), and high doses of MIBG (sometimes used in the treatment of neuroblastoma) may also result in low or absent levels of thyroid hormone, depending on the amount of thyroid tissue removed or destroyed.

People who received radiation that may have affected the thyroid gland directly are at risk for primary hypothyroidism, thyroid nodules, and/or thyroid cancer. People who received radiation to the thyroid gland are also at risk for hyperthyroidism. Radiation to the following areas have the potential to affect the thyroid gland:

  • Head/ brain (cranial)
  • Nose, mouth, and/or throat (nasopharyngeal, oropharyngeal)
  • Neck (cervical, supraclavicular, mantle, or mini-mantle)
  • Upper chest (whole lung, mediastinum)
  • Spine (cervical/ neck portion)
  • Total body irradiation (TBI)

People who received radiation to areas that may have affected the pituitary gland in the brain are at risk for central hypothyroidism. These areas include:

  • Head/ brain (cranial)
  • Eye/ orbit
  • Ear/ infratemporal region (midfacial area behind the cheekbones)
  • Nose, mouth, and/or throat (nasopharyngeal, oropharyngeal)

Other factors that have been shown to increase the risk of thyroid problems after childhood cancer include being:

  • Female
  • Treated with higher radiation doses
  • Treated at a young age

Thyroid problems may occur soon after radiation but generally do not occur until several years later. If treated promptly, thyroid problems are easily managed.

What Survivors Can Do

Regular check-ups

Survivors should have yearly check-ups. 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.

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 because 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.

Treatment of thyroid problems

If problems with thyroid levels are identified, health care providers may refer survivors to an endocrinologist (hormone specialist) for continuing evaluation and management.

Treatment of 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.

Treatment of hyperthyroidism

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 radioactive liquid iodine called (I-131)) may be done.
  • Surgery to remove the thyroid gland is another treatment.

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

Treatment of thyroid nodules

Thyroid nodules need additional testing. This is generally done with an ultrasound and, if indicated, ultrasound-guided biopsy. There are different treatment options for thyroid nodules and thyroid cancer.

Reviewed: June 2018