Thyroid Nodules and Follicular Cell-Derived Thyroid Carcinomas in Children.

Although pediatric thyroid tumors have many similarities to those occurring in adults, significant differences are also recognized. For example, although thyroid nodules in children are much less common than in adults, a higher percentage is malignant. Moreover, while pediatric papillary thyroid carcinoma (PTC) is associated with more advanced disease, death due to disease in children and adolescents is very rare, even when distant metastases are present. Some subtypes of thyroid carcinoma, like diffuse sclerosing variant, are especially common in children and adolescents. Moreover, certain histologic findings, such as a tall cell morphology or increased mitotic activity, may not carry the same prognostic significance in children as in adults. Recent studies exploring the molecular underpinnings of pediatric thyroid carcinoma indicate that while driver alterations of thyroid tumorigenesis in children and adults are essentially the same, they occur at very different frequencies, with translocation-associated tumors (most commonly harboring RET and NTRK fusions) comprising a sizable and distinct group of pediatric PTC. DICER1 mutations, an infrequent mutation in adult thyroid tumors, are relatively frequent in pediatric encapsulated follicular-patterned thyroid tumors (with or without invasion or nuclear features of PTC). Additionally, tumor predisposition syndromes (most notably DICER1 syndrome and PTEN hamartoma tumor syndromes such as Cowden syndrome) should be considered in children with thyroid tumors, especially follicular-patterned thyroid tumors and poorly differentiated thyroid carcinoma. This review will explore the current state of knowledge of thyroid nodules and carcinomas in children and adolescents.