10210- CS-11 A CASE OF DIFFUSE HEMISPHERIC GLIOMA WITH H3 K27M MUTATION, NEC

Abstract Reports of diffuse glioma with H3 K27M mutation occurring in non-midline regions are rare. We report a case of diffuse hemispheric glioma with H3 K27M mutation (DHG) that infiltrated both temporal lobes without involvement of midline structures. The patient was a 50-year-old man who was found to have intracranial lesions during a brain checkup. MRI showed diffuse FLAIR high signal lesions in the right temporal lobe-hippocampus-insular cortex and the medial contralateral temporal lobe. A partial resection of the right temporal lobe was performed, and pathology showed moderately dense infiltrating atypical glial cells on HE staining. Immunostaining was positive for p53 and H3 K27M, negative for ATRX and H3K27me3, and Ki67 was 25.7% at a hot spot. Cancer panel test confirmed H3 K27M and TP53 mutations, as well as PDGFRA amplification. Based on these findings, the patient was diagnosed with diffuse hemispheric glioma, H3 K27M mutation, not elsewhere classified (NEC). The patient underwent postoperative radiation therapy (60 Gy/30 fractions) with concomitant and 12 courses of maintenance temozolomide therapy. At 18 months post-surgery, MRI showed progression of the FLAIR lesion and the appearance of some enhancing lesions, so gamma knife surgery was performed. The patient is currently under observation 21 months after surgery. Including this case, 12 cases of DHG, have been reported, with a median age of 44 years, older than diffuse midline glioma, H3 K27M mutant (DMG). Additionally, MAPK pathway alteration was observed in 42% of cases, and three patients had an overall survival of more than two years, indicating the presence of long-term survivors. Although the differences between DHG and DMG are unclear, DHG may exhibit clinical and molecular biological characteristics from DMG. Further accumulation of cases and studies is necessary to clarify these differences.