The Mutation Is Not a Risk Factor for More Aggressive Tumor Behavior in Radiogenic and Sporadic Papillary Thyroid Carcinoma at a Young Age.

Histopathological changes in the fusion oncogene-driven papillary thyroid carcinomas (PTCs) from children and adolescents exposed to Chernobyl fallout have been extensively studied. However, characteristics of the radiogenic BRAF-positive PTCs, whose proportion is growing with time, are not well described yet. We analyzed the relationship between the BRAF status (determined immunohistochemically with the VE1 antibody) and the clinicopathological features of 247 radiogenic and 138 sporadic PTCs from young Ukrainian patients aged ≤28 years. The frequency of BRAF was increasing with patient age, consistently remaining lower in radiogenic PTCs. In both etiopathogenic groups, the BRAF-positive PTCs more frequently had a dominant papillary growth pattern, smaller tumor size, higher Ki67 labeling index, and a frequency of the major indicators of tumor invasiveness that is lower than or equal to that of the BRAF-negative tumors. Comparison of the BRAF-positive PTCs across the groups found a virtual absence of differences. In contrast, the BRAF-negative radiogenic PTCs displayed less frequent dominant papillary and more frequent solid growth patterns, lower Ki67 labeling index, and higher invasiveness than the BRAF-negative sporadic tumors. Thus, BRAF is not associated with a more aggressive course of PTC in young patients regardless of etiology. The major clinicopathological differences between the radiogenic and sporadic PTCs are observed among the BRAF-negative tumors.