Supplementary Material for: IDH-mutant WHO Grade 4 Astrocytoma with BCOR Alteration

BCOR, a transcriptional regulator, has been increasingly recognized for its involvement in various human cancers, where it plays a significant role in neoplastic transformation and tumor progression. As a component of the noncanonical polycomb repressive complex 1 (PRC1), BCOR contributes to transcriptional repression through histone modifications. BCOR alterations have been also identified in some brain tumors, with mutations such as nonsense, frameshift, and splice site alterations reported in glial tumors, astroblastomas, pineoblastomas, and medulloblastomas. While BCOR alterations have not previously been reported in IDH-mutant WHO grade 4 astrocytoma, we describe a rare case involving an adult patient who presented with a recurrent, contrast-enhancing tumor in the left parietal region. Following complete surgical resection, the biopsy confirmed an IDH-mutant WHO grade 4 astrocytoma. Next-generation sequencing (NGS) using the TruSight Oncology 500 (TSO500) platform, which included both DNA and RNA sequencing, revealed mutations in IDH1, ATRX, and EGFR, alongside a novel BCOR internal tandem duplication (ITD). This discovery highlights a unique finding of BCOR alteration in an IDH-mutant WHO grade 4 astrocytoma. The presence of a BCOR ITD in this context expands the molecular spectrum of high-grade astrocytomas and suggests the need for further investigation into its potential implications for tumor behavior, prognosis, and therapeutic targeting.