HGG-33. HIGH GRADE TRANSFORMATION OF CNS TUMOR WITH BCOR:CREBBP FUSION: A CASE REPORT

Abstract

Abstract BACKGROUND The discovery of unique EP300:BCOR and CREBBP:BCORL1 fusions has extended the spectrum of BCOR altered CNS tumors previously associated with BCOR internal tandem duplication (ITD). Due to the rarity of CNS tumors with BCOR alterations, there is limited information on the clinical outcomes and the effective treatment strategies. METHODS Literature review and retrospective chart analysis RESULTS An 18-year-old male who presented with seizures was found to have a left temporal mass. Histologic diagnosis was low grade glioneural tumor harboring a pathogenic CREBBP:BCOR1 fusion, matching to CNS tumor with EP300:BCOR/BCORL1 fusion by methylation. A re-resection aimed at gross total resection was then performed. Histologic examination revealed residual glioma with focal high-grade transformation, Ki67 up to 35% and CDKN2A loss via FISH analysis. The patient was treated with focal radiation to 54Gy. He remains disease- and seizure-free 1 month post radiation therapy. This case displayed some similarities to previously reported cases, including oligodendroglial- or ependymoma-like features, positivity for Olig2 and/or GFAP, presence of calcifications, and branching capillary networks. However, this case had less frequent mitoses than previously reported cases. In a series of 21 patients with BCOR altered tumors, BCOR-fusion tumor patients had a more favorable PFS compared to BCOR-ITD tumors. In a reported case series of high grade BCOR altered CNS tumors, 5 out of 8 patients remained alive, all of whom received radiation therapy as a primary treatment or at relapse. There is one prior report of an EP300:BCOR tumor undergoing high-grade transformation; increased mitoses, cellularity, and necrosis were observed. This case was lacked necrosis. CONCLUSIONS The optimal treatment for BCOR altered tumors of the CNS is largely unknown given the limited reported cases. Radiation therapy in addition to gross total resection may be an effective treatment leading to more favorable PFS and OS.