Diffusely infiltrating glioma with CREBBP–BCORL1 fusion showing overexpression of not only BCORL1 but BCOR : A case report

BCORL1 encodes a transcriptional corepressor homolog to BCOR. BCORL1 rearrangements have been previously described as rare events, and among them, CREBBP–BCORL1 has been reported only in 2 cases of ossifying fibromyxoid tumors. Herein, we present the first case of diffusely infiltrating glioma with CREBBP–BCORL1 involving a 17-year-old female patient. Histologically, the tumor was composed of a diffusely infiltrative proliferation of small tumor cells with moderate cellularity showing prominent microcystic formation. DNA methylation analysis revealed that the current case and a previously reported anaplastic ependymoma with EP300 – BCORL1 were clustered together in close proximity to but distinct from methylation class high-grade neuroepithelial tumor with BCOR alteration. RNA sequencing demonstrated high mRNA expression of not only BCORL1 but BCOR , and the latter was compatible with diffuse nuclear expression of BCOR detected by immunohistochemistry. Our findings suggest that central nervous system tumors with CREBBP / EP300 - BCORL1 may exhibit diverse morphologies but form a distinct DNA methylation group and that BCORL1 fusion genes may lead to upregulation of both BCOR and BCORL1 .