Supplementary Material for: Molecular Characterization and Phenotype-Genotype Correlation of Childhood Thyroid Nodules and Cancers: A study of 62 patients

Introduction: Pediatric thyroid nodules and cancer are uncommon but have significant challenges in clinical management due to potential malignancy. Understanding the genotype-phenotype correlation helps in enhancing patient care and personalized treatment strategies. Methods: Our study aimed to determine the molecular characterization of thyroid nodules and cancer in childhood and investigate the genotype-phenotype relationship. The Bethesda Category (BC) is a standardized framework for classifying thyroid fine-needle aspiration (FNA) results. We conducted a retrospective analysis of clinical data, including next-generation sequencing (NGS), from pediatric thyroid nodule and cancer patients. Analysis was conducted using samples from a pathology archive and follow-up clinical data from a tertiary care center. Results: A cohort of 62 pediatric patients (50 female, 12 male) aged 2.67-19.61 years (mean 14.18 ± 3.45 years), evaluated over a mean follow-up period of 5.06 ± 3.99 years. NGS analysis of 34 genes for DNA variants and RNA sequencing for gene fusions in BC II-VI samples. Of 62 patients, 37 (59.7%) had differentiated thyroid cancer (DTC), 14 (22.6%) had benign findings, and 9 (14.5%) were categorized as other. Pathogenic variants were found in 80% of DTC patients, with BRAFV600E being the most common (37%). RET, NTRK, and ALK fusions were present in 32% of DTC patients. In the benign group, variants in DICER1, TSHR, and PTEN were noted. Pathogenic variants were also identified in BC-II to BC-IV patients that later developed DTC. High-risk DTC patients included those with BRAFV600E and NCOA4-RET fusions. Conclusions: BRAFV600E and gene fusions involving RET, NTRK, and ALK were the most frequent pathogenic findings in pediatric DTC, with implications for risk stratification and tailored management. Early molecular analysis can guide prognosis and treatment in patients with initial benign or indeterminate diagnoses.