HGG-49. A PEDIATRIC THALAMIC HIGH-GRADE GLIOMA WITH H3F3A K27M AND BRAF V600E DOUBLE MUTATIONS

Abstract CASE A 18-month-old boy presented with approximately 2 months history of progressive left hemiparesis and left exotropia. MRI study showed a 3–4 cm T1-iso, T2-high tumor at right thalamus to midbrain with little contrast enhancement. The patient underwent endoscopic biopsy of the tumor, which showed relatively dense proliferation of small cells with round nuclei, mitosis of the tumor cell, but no necrosis. Immunohistochemical showed positive stain of GFAP and Olig2. Ki-67 was 34%. The histopathological diagnosis was compatible with high grade glioma. Chemotherapy with vincristine, cyclophosphamide, cisplatin and etoposide was initiated. Molecular testing of the tumor revealed H3F3A K27M and BRAF V600E double mutations in DNA from frozen tumor tissue. DISCUSSION The concurrent mutation of H3F3A K27M and BRAF V600E in pediatric glioma is very rare, but there are several cases previously reported in literature. Interestingly those cases are heterogenous in age, location, histopathological subtypes and clinical outcome.