Pediatric Thyroid Cancer Overview

Thyroid cancer occurs in all age groups, from children and adolescents through seniors but remains a rare disease in children less than age 10, with an annual incidence of less than one per million. It is more common in older children and adolescents, with 15.4 cases per million per year in 15-19 year olds. It has a peak incidence at age 50 and beyond.

The number of female adolescents with thyroid cancer has slightly increased in the United States in recent years. Males and young children under age 15 have had no increase in incidence over the last several decades.

The two main types of pediatric thyroid cancer are:

(1) Differentiated Thyroid Cancer: This includes papillary and follicular thyroid cancer and their variants. Papillary thyroid cancer is the most common type in both children and adults.

(2) Medullary Thyroid Cancer: About 30% to 35% are familial tumors transmitted by a gene from either the mother or father.

More About Differentiated Pediatric Thyroid Cancer:

I. Papillary and Follicular

• Because of the lack of prospective research, differentiated thyroid cancer in children and adolescents generally is managed similarly to that in adults. Papillary thyroid cancer is the type of tumor that affects children in the vast majority of cases and which, compared with other types of thyroid cancer, has the best prognosis.
  
  
• Each case is approached individually, to fit the needs of each patient. In children and adolescents, papillary thyroid cancer tends to be more advanced at the time of diagnosis than it is in adults with the same disease.

• The majority of children with papillary thyroid cancer have local spread to the lymph nodes of the neck at the time the thyroid cancer is diagnosed. About 10% to 20% of the children have distant metastases, most commonly to the lung, compared with only 5% of the adults with this disease.

• Recurrence of papillary thyroid cancer is more common in children than it is in adults. However, despite higher rates of recurrence and more widespread disease at presentation, the prognosis is excellent with appropriate treatment.

• Follicular thyroid cancer, which is rare in children, has been reported to demonstrate more aggressive characteristics and poorer prognosis due to vascular invasion. Still, the prognosis is better for children than for their adult counterparts who present with a similar extent of disease.

II Follicular Thyroid Cancer.

• Follicular thyroid cancer is not very common in childhood. The primary tumor is usually a single lesion within the thyroid gland. Lymph node metastases can occur with less differentiated variants of follicular thyroid cancer but are not generally expected.

• It is associated with a worse prognosis (as compared to papillary thyroid carcinoma) due to its propensity for vascular invasion, which increases the risk of metastases to distant sites of the body, such as the lungs and bones.

• Very few children die from this disease. Even those children with distant metastases at diagnosis can anticipate survival for years to decades. The goals of treatment are to eliminate the disease and to reduce the chance of recurrence. Sometimes the disease cannot be entirely eradicated, and therefore, another therapeutic goal is to achieve stable disease and no symptoms of disease.

Statistics on Differentiated Pediatric Thyroid Cancer:

• Papillary and follicular thyroid cancer accounts for only approximately 1% of all pediatric cancers in the 5-9 year old age group and up to 7% of cancers in the 15-19 year old age group. Only 1 in a million children younger than age 10 years will get thyroid cancer.

• In children under age 10, thyroid cancer tends to affect boys and girls with about equal frequency, but thereafter it generally becomes more common in girls. The ratio of girls to boys with differentiated thyroid cancer reaches a peak of over 5 to 1 in the 15-to-20 year-old age group.

• Medullary thyroid carcinoma (MTC) accounts for 5% to 10% of all thyroid cancers. In children and adolescents, it is a very rare disease, affecting less than one child per million per year.
  
  

Pediatric Thyroid Cancer Causes

As the National Cancer Institute notes, no one knows the exact causes of thyroid cancer. Doctors can seldom explain why one person gets this disease and another does not. Research has shown that people with certain risk factors are more likely than others to develop thyroid cancer.

The following risk factors are associated with an increased chance of developing pediatric Thyroid Cancer:

• For differentiated thyroid cancer, a risk factor is exposure at a young age to ionizing radiation, whether from ingestion of radioactive iodines (iodine is the building block of thyroid hormones) or external radiation, as used to treat some childhood cancers. The main example of this was the increased rate of thyroid cancer identified in children following the 1986 Chernobyl nuclear power plant accident.
  
  
• In general, the differentiated thyroid carcinomas are not diseases that are passed from one generation to the next. However, there are some hereditary forms of the disease, although the exact cause of the disease in these families is not yet known. Some genetic syndromes such as Gardner syndrome and the Carney complex can have papillary thyroid carcinoma as part of the spectrum of disease.

• Some follicular thyroid carcinomas can be associated with a mutation in the PTEN gene, which causes Cowden syndrome. Gene mutations (RET/PTC, BRAF, among others) that cause differentiated thyroid cancer have also been identified within tumor cells. These mutations are not in all cells of the body and therefore are not expected to be hereditary.

• In children and adolescents, medullary thyroid cancer is almost always the familial form, meaning that it is due to a specific mutation (defect) in the DNA of the cells of the body. This mutation occurs in a gene called the RET proto-oncogene.