DNAR-12. High-grade IDH-mutant astrocytomas are characterized by chromothripsis and nuclear envelope instability compared to IDH-mutant oligodendrogliomas

Abstract IDH-mutant gliomas include astrocytomas and oligodendrogliomas (ODG) that share a common glial precursor and IDH1/2 gene mutation. However, those entities display markedly distinct biological behaviors and clinical outcomes. Whereas ODG display relative genomic stability and are associated with favorable prognosis, astrocytomas often progress to highly aggressive forms characterized by extensive genomic rearrangements. Chromothripsis (CT), defined as a catastrophic one-off shattering and chaotic repair of one to two chromosomes, may drive abrupt genomic remodeling. Hypotheses regarding CT origin include mitotic errors such as chromosome entrapment in micronuclei, nuclear envelope rupture or chromosomal bridges. The incidence and mechanisms of CT events in IDH-mutant gliomas remain largely unexplored. To address those issues, we analyzed 235 IDH-mutant gliomas (143 astrocytomas, 92 ODG). We identified CT events using high-resolution SNP arrays and CTLPScanner algorithm, with cross-validation by visual inspection. Nuclear instability was investigated by confocal immunofluorescence microscopy on formalin-fixed paraffin-embedded sections, employing DAPI for nuclei/micronuclei, anti-lamin A/C and B1 antibodies to assess nuclear envelope (NE) integrity, and anti-BAF antibodies to show nuclear rupture or repair. Imaging employed Z-stack acquisition on a Leica TCS SP8 and analysis with FIJI. CT was observed exclusively in high-grade (WHO grade 3/4) astrocytomas (11/142, 7.8%; 7 grade 3 tumors and 4 grade 4 tumors), with higher frequency in higher-grade tumors (15% of grade 4 vs 7.6% of grade 3 astrocytomas). CT was not detected in either ODG or grade 2 astrocytomas. CT-positive tumors harbored more micronuclei and more frequent NE disruption, evidenced by anti-lamin A/C and anti-BAF immunopositivity. Thus, high-grade IDH-mutant astrocytomas were characterized by CT events and NE instability compared to lower-grade astrocytomas and ODG. Those phenomena may underlie the less favorable prognosis of astrocytomas compared to ODG.