By Andrew J. Bauer, M.D. and Gary L. Francis, M.D., Ph.D., Reprinted, with permission, from pages 98-100 of "Thyroid Cancer in the Child and Adolescent," which is Chapter 12 of the book "Thyroid Cancer: A Guide for Patients", (Douglas Van Nostrand, M.D., Gary Bloom, and Leonard Wartofsky, M.D., editors, Keystone Press, 2010.) See http://www.thyca.org/about/TCGuide/.
In evaluating thyroid nodules, we often separate children into two groups: prepubertal (before the onset of puberty) and postpubertal (after puberty has begun). This is not absolute, but it does allow us to make several distinctions.
Both groups look perfectly healthy except for the finding of a lump (nodule) in the thyroid and frequently swollen lymph glands in the neck. This lack of symptoms can make it more difficult to accept that a thorough evaluation (blood tests, ultrasound and tissue biopsy) is needed. In general, prepubertal children appear to have an increased risk of having thyroid cancer and a greater chance of having a family or genetic risk factor (a history of thyroid disease or a medical condition associated with thyroid disease).
In teenagers, thyroid disease including hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), and thyroid nodules are more common, and girls have thyroid disease more frequently than boys.
It is also during the late teenage years that survivors of non-thyroid childhood cancers who received radiation therapy as part of their treatment protocols develop thyroid disease.
The thyroid gland is particularly sensitive to radiation exposure, and the younger the patient at the time of radiation therapy, the more quickly thyroid disease may develop.
After radiation exposure, the prevalence of thyroid disease (hypothyroidism, nodules and/or cancer) is up to 40-fold higher with patients developing problems as soon as five years or as late as 30 years after the initial treatment.
Why do children develop thyroid cancer?
Children who have been exposed to radiation are at increased risk for thyroid nodules and thyroid cancer largely because the thyroid gland is sensitive to the effects of radiation.
Before 1980, many children received radiation therapy for a variety of medical conditions to include ringworm of the scalp, facial acne, an enlarged thymus gland, and a host of other conditions. While these practices have been abandoned, what has been learned from these experiences is that the younger the child at
he time of exposure, the greater the chance and the shorter the time for the child to develop thyroid cancer.
In addition, small radiation doses relative to larger doses appear to have a greater chance of causing thyroid abnormalities such as cancer. This is because larger doses usually kill all the cells whereas smaller doses damage the DNA of the cell. This damage (DNA mutations) increases the risk of unregulated growth, leading to the development of thyroid nodules and/or cancer.
Children being treated for other forms of childhood cancer, such as brain tumors, leukemias, and lymphomas, may still receive radiation exposure to the thyroid. Doses as small as 50 rads (1 rad = 1 cGy or 100 rad = 1 Gy) may cause enough damage to increase the risk of thyroid nodules and thyroid cancer, with the greatest risk occurring in patients who have received radiation doses of 200 to 2,000 cGy (or rads) to the head and neck before age 10.
In total, thyroid cancer may develop in as many as 10 percent of all cancer survivors following radiation treatments.
Most thyroid disease requires about 15 years to appear, but cases have been reported after as long as 30 years or as short as five years in younger children. What makes the child's thyroid gland more susceptible to radiation damage when compared to an adult's is not known.
Childhood cancer survivors
One subset of children at an increased risk of developing thyroid nodules and thyroid cancer are children who have been exposed to radiation. Before 1980, many children received radiation therapy for a variety of medical conditions to include ringworm of the scalp, facial acne, an enlarged thymus, and a whole host of other conditions. While these practices have been abandoned, what has been learned from this experience is that the younger the child at the time of exposure, then the greater the chance and the shorter the time for the child to develop thyroid cancer. In addition, small radiation doses appear to have a greater chance than larger doses of causing thyroid abnormalities such as cancer. This is so because larger doses usually kill all the cells whereas smaller doses cause damage to the nuclear genetic apparatus of the cell, which causes mutations through defective repair, which in turn increases the risk of developing thyroid nodules and/or cancer.
Today the children who may still receive radiation exposure to the thyroid are those who are being treated for other forms of childhood cancers such as brain tumors, leukemias, and lymphomas. Doses as small as 50 rads may cause enough damage to increase the risk of thyroid nodules and thyroid cancer, with the greatest risk occurring in patients who have received radiation doses of 200 to 2,000 cGy or rads to the head and neck prior to the age of 10 years.
In total, thyroid cancer may develop in as many as 10 percent of all tumor survivors after radiation treatments with an increasing risk related to the younger age the child was when they received radiation therapy. Most thyroid disease requires about 15 years to appear, but cases have been reported as late as 30 years after, or as short as five years later in younger children. What makes the child's thyroid gland more susceptible to radiation damage when compared to an adult's is not known.
Radiation exposure from the environment
One concern is the widespread increase in thyroid cancer among children exposed to environmental radiation. An extreme example of this is the Chernobyl nuclear accident in Belarus in April 1986. After the accident, childhood thyroid cancers began to appear within five years. Because thyroid cancers usually develop slowly, the full impact of this accident is just now being realized, some 20 years later.
In the event of a nuclear accident, there are preventive measures that can be taken against radiation damage to the thyroid gland. These include the provision of stable iodine and water, milk, and food that are not contaminated with radioactivity.
If a known radiation event occurs the World Health Organization recommends giving stable iodine in doses of 0.1 gm/day to adults, 0.05 gm/day to children over 3 years of age and 0.025 gm/day to children under 3 years of age. These doses should be given until food, water, and milk are free of contamination of radioactivity.
Other inherited thyroid cancer syndromes
Some forms of papillary thyroid cancer (PTC) are inherited (passed from one generation to the next). In affected families, inheritance follows a dominant mode of transmission (one parent passes on the risk of cancer while the other does not). These inherited causes should be considered in any family with cancer affecting multiple generations or those in which cancer syndromes such as Gardner’s syndrome, Cowden’s syndrome, and the Carney complex have been observed.
Last updated: January 3, 2012