Cerebellar Diffuse Midline Glioma, H3 K27M-Mutant in an Adult Patient: Case Report (P5.160)

Objective: OBJECTIVE: Describe a case of an adult patient with a cerebellar diffuse midline glioma, H3 K27Mmutant. Background: BACKGROUND: Diffuse midline gliomas H3 K27M-mutant gliomas are primarily pediatric neoplasms typically located brainstem, particularly the pons. Adult diffuse midline gliomas have been described in the thalamus and spinal cord. The presence of the H3 K27M mutations is associated with a poor prognosis. Optimal adjuvant treatment after maximal surgical resection and radiotherapy is unknown. Design/Methods: DESIGN/METHODS: A 45 year-old man presented with a two-day history nausea, headaches, and ataxia. Imaging revealed a cerebellar mass with partial obstruction of the 4th ventricle and subtle T2 signal involving the right middle cerebellar peduncle and basis pons concerning for infiltrating tumor. Results: RESULTS: The patient was treated with a right sub-occipital craniectomy with tumor resection. Neuropathology review revealed a high grade glial neoplasm which was positive for Olig2, IDH1 wild- type, and ATRX intact on immunohistochemistry. The tumor cells expressed H3 K27M-mutant protein consistent with a diagnosis of diffuse midline glioma, H3 K27M-mutant. He had a poor performance status, and the patient's family and multidisciplinary team recommended a short course of palliative radiotherapy and discharge to hospice care. Conclusions: CONCLUSION/DISCUSSION: Diffuse midline gliomas, H3 K27M-mutant, are very rare in adults and typically occur in midline locations including the spinal cord and thalamus. To our knowledge this is the first reported case of a primarily cerebellar diffuse midline glioma with an H3 K7M mutation. Identification and reporting of clinical, pathologic, and treatment outcomes of adult cases may aid in the development of adjuvant treatment strategies.