The use of multimodal therapy optimizes the chances for survival with over 70% of children expected to survive 5 or more years following initial diagnosis.[28,37]
The annual incidence of thyroid cancers is low in children younger than 15 years (2.0 per 1 million people), accounting for approximately 1.5% of all cancers in this age group. Thyroid cancer incidence is higher in children aged 15 to 19 years (17.6 per 1 million people), and it accounts for approximately 8% of cancers arising in this older age group. Most thyroid carcinomas occur in girls.
There is an excessive frequency of thyroid adenoma and carcinoma in patients who previously received radiation to the neck.[44,45] In the decade following the Chernobyl nuclear incident, there was a tenfold increase in the incidence of thyroid cancer compared with the previous and following decades. In this group of patients with exposure to low-dose radiation, tumors commonly show a gain of 7q11. When occurring in patients with the multiple endocrine neoplasia syndromes, thyroid cancer may be associated with the development of other types of malignant tumors. (Refer to the Multiple Endocrine Neoplasia (MEN) Syndromes and Carney Complex section of this summary for more information.)
Tumors of the thyroid are classified as adenomas or carcinomas.[48,49,50,51,52] Adenomas are benign growths that may cause enlargement of all or part of the gland, which extends to both sides of the neck and can be quite large; some tumors may secrete hormones. Transformation to a malignant carcinoma may occur in some cells, which then may grow and spread to lymph nodes in the neck or to the lungs. Approximately 20% of thyroid nodules in children are malignant.[48,53]
Various histologies account for the general diagnostic category of carcinoma of the thyroid:[45,54]
- Papillary carcinoma (60%–75%): Papillary carcinoma often has multicentric origin and a very high rate of lymph node metastasis (70%–90%). Papillary carcinoma (often referred to as differentiated thyroid cancer) generally has a benign course, with a 10-year survival rate of more than 95%.[55,56] Overall, long-term outcomes for children and adolescents with papillary thyroid cancer are excellent, with 2% cause-specific mortality at 40 years.
- Follicular carcinoma (10%–20%): Follicular carcinoma is usually encapsulated and has a higher incidence of bone and lung metastases. It may be sporadic or familial. Follicular carcinoma (often referred to as differentiated thyroid cancer) generally has a benign course, with a 10-year survival rate of more than 95%.
- Medullary carcinoma (5%–10%): Medullary carcinoma is usually familial.
- Anaplastic carcinoma (<1%).
Studies have shown subtle differences in the genetic profiling of childhood differentiated thyroid carcinomas compared with adult tumors. A higher prevalence of RET/PTC rearrangements is seen in pediatric papillary carcinoma (45%–65% vs. 3%–34% in adults). Conversely, BRAF V600E mutations, which are seen in more than 50% of adults with papillary thyroid carcinoma, are extremely rare in children.