THYROID TUMORS AND CANCER
Thyroid carcinoma is the most common endocrine tumor in children (and in adults); approximately 10% of thyroid cancers are diagnosed before 19 years of age. Similar to adults, the most common presentation is an asymptomatic nodule noted on physical examination; however, thyroid nodules are reported much less frequently in children, and the risk of malignant disease appears to be much higher, with 20% to 25% of pediatric nodules found to have carcinoma compared with 10% to 14% of adults.1 In addition, at diagnosis, approximately 60% of children have regional lymph node metastasis, and up to 15% to 20% with lateral lymph node metastasis will have pulmonary metastasis.2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18
There is some suggestion that two subpopulations within pediatrics warrant greater concern secondary to an increased incidence and/or invasiveness of disease: children diagnosed with thyroid cancer prior to 10 years of age and children with a history of previous radiation exposure. The most commonly cited risk of radiation exposure is related to therapeutic treatment of oncologic disease, where there may be as high as a 27- to 53-fold increase in the risk of developing thyroid nodules and differentiated thyroid carcinoma (DTC).19,20,21 There is less data in regard to the risk of thyroid nodules and thyroid cancer developing in patients exposed to repeated diagnostic imaging, however, a recent review suggested that even low-dose computed tomography (CT) may be associated with an increased risk of cancers, estimated at 1.10 per 100,000 person years compared to unexposed patients, with a dose-response relation.22 Irrespective of the etiology, age at diagnosis, or degree of metastasis, with appropriate preoperative staging, stratified but complete surgical intervention, and selected use of radioiodine (RAI) treatment to treat persistent, non-surgical disease, children and adolescents with DTC experience 95% to 98% long-term survival.23,24 Lifelong monitoring is essential, as up to 30% of cancers may recur, at times years after achieving remission.25
Differentiated thyroid carcinoma (DTC) is the most common form of thyroid cancer in children; 85% to 90% of these tumors are papillary thyroid carcinomas (PTCs), whereas the rest are follicular thyroid carcinomas (FTCs).26 In children with a history of radiation exposure, both PTCs and FTCs are found, but similar to spontaneous tumors, the majority of radiation-induced thyroid cancers have PTC-like histological characteristics.27 It has become clear that the thyroid gland in children exhibits increased sensitivity to small doses of radiation; in addition, the latency with which a child develops thyroid nodules or cancer decreases the younger the child is at the time of radiation exposure.28,29
FTC is more common in the adolescent age group compared with children ...