Exploring the Molecular Features and Clinicopathological Correlations of Diffuse Sclerosing Papillary Thyroid Carcinoma.

The diffuse sclerosing variant of papillary thyroid carcinoma (DSV-PTC) is a rare, aggressive subtype with distinct clinicopathological features. This study aimed to characterize its molecular alterations and evaluate their clinical associations. A retrospective analysis of 51 DSV-PTC cases was conducted. Clinicopathological data were reviewed, and molecular profiling was performed using fluorescent PCR to detect mutations and gene fusions across 12 thyroid cancer-related genes. This study included eight paediatric cases (15.7%) and 43 adult cases (84.3%) of DSV-PTC. The most common alteration was BRAF mutation (39.2%), followed by RET fusions (25.5%; including CCDC6-RET in 23.5% and NCOA4-RET in 2.0%), ETV6-NTRK3 fusion (5.9%) and TERT promoter mutations (2.0%). Compared with BRAF-mutated tumours, RET fusion-positive cases showed significantly larger primary tumours (p = 0.016), larger metastatic nodes (p = 0.009) and higher T stages (p = 0.046). Paediatric patients exhibited more aggressive features, such as higher rates of lateral neck metastasis and extrathyroidal extension, but had fewer BRAF mutations. The overall recurrence rate was 15.7%, with earlier recurrence in RET fusion cases. One patient with coexisting ETV6-NTRK3 fusion and TERT mutation progressed to anaplastic thyroid carcinoma and died of disease. DSV-PTC demonstrates substantial molecular heterogeneity. RET fusions are linked to more aggressive behaviour, and paediatric cases often show extensive locoregional spread. Coexisting NTRK and TERT alterations may signal high-risk progression, highlighting the value of molecular stratification in management.