Abstract BACKGROUND Pediatric high grade glioma (HGG) have a dismal prognosis despite aggressive treatment. In this report, we discuss a patient with HGG successfully treated with combination of resection, radiotherapy, chemotherapy, and biologic therapy. RESULTS An 8-year-old male presented with intermittent headaches, vomiting and fatigue. Imaging demonstrated four solid/cystic enhancing intra-axial lesions within the left cerebral hemisphere- two within the left frontotemporal region, one in the superior parietal region, and one in the temporal lobe, all with perilesional edema and resultant subfalcine herniation with midline shift. The patient underwent subtotal resection of the frontotemporal and parietal lesions. Histopathology was consistent with glioblastoma. Whole exome sequencing revealed alterations in TP53, ATRX, PTEN, TSC2 as well as subclonal mutation in NF1. The tumor was unable to be further classified by DNA methylation. However histopathologic and molecular findings support the diagnosis of diffuse pediatric-high grade glioma, H3-wildtype and IDH-wildtype. The patient received adjuvant 59.4 Gy focal proton therapy with concurrent temozolomide and maintenance chemotherapy with temozolomide and lomustine for 6 cycles. End of therapy imaging demonstrated complete resolution of all sites of disease. Due to high likelihood of recurrence, the patient was subsequently started on targeted therapy with everolimus and ribociclib which continue to be well tolerated without dose adjustments. The patient remains stable and without recurrence 2.5 years since diagnosis, and 15 months since initiation of biologic therapy. Additionally, the patient underwent testing for cancer predisposition which revealed presence of TP53 heterozygous mutation consistent with Li-Fraumeni syndrome. The patient remains without other malignancies on surveillance imaging per LFS guidelines. CONCLUSION Our case report illustrates the value of both chemotherapy and biologic therapy in treatment of HGG. In addition to this, it emphasizes the importance of germline testing for cancer predisposition in patients with high grade tumors.

HGG-43. DIFFUSE PEDIATRIC HIGH GRADE GLIOMA SUCCESSFULLY TREATED WITH MULTIMODAL THERAPY