Diffuse low-grade glioma with a rare BRAF p.T599dup mutation in a child: importance of clinicopathological and molecular correlation.

backgroundBRAF mutations are key genetic alterations in pediatric gliomas, especially within the MAPK pathway-altered category of the 2021 WHO classification. The BRAF p.T599dup mutation is an extremely rare in-frame insertion reported in melanoma, thyroid, and lung carcinoma, and occasionally in pleomorphic xanthoastrocytoma or ganglioglioma. However, diffuse low-grade glioma harboring this mutation has not been well characterized. CASE PRESENTATION: An 8-year-old boy presented with a four-year history of seizures. MRI revealed a right temporal mass with a cystic component, and gross total resection was achieved. Histologically, the tumor showed diffuse infiltration of mildly atypical Olig2- and GFAP-positive glial cells without mitosis, microvascular proliferation, or necrosis. Sanger sequencing identified a rare BRAF p.T599dup mutation, whereas IDH1/2 and FGFR1 were wildtype. The tumor was diagnosed as diffuse low-grade glioma, MAPK pathway-altered, harboring BRAF p.T599dup. The patient has remained seizure-free and recurrence-free for 30 months without adjuvant therapy.

conclusionThis case represents one of the few diffuse low-grade gliomas harboring BRAF p.T599dup and provides detailed clinicopathological and molecular characterization of this rare alteration. The tumor closely resembled BRAF p.V600E-mutated gliomas, highlighting the diagnostic and therapeutic implications of recognizing such rare BRAF variants and the importance of integrating clinicopathological and molecular data for accurate classification.