BIOM-32. GENOMIC DETERMINANTS OF DIFFUSELY INFILTRATIVE GLIOMATOSIS CEREBRI PATTERN

Abstract Gliomatosis cerebri (GC), though no longer a distinct pathological entity in WHO 2021, is a unique and aggressive phenotype of diffuse gliomas with extensive and widespread infiltration. GC can present as primary de novo or secondary after treatment. We aimed to study the genomic determinants of GC. We identified 72 GC cases from 2013-2023 at MD Anderson Cancer Center. Cases were confirmed by detailed radiographic review. This included 57 glioblastoma (79%), 13 IDH mutant astrocytoma (18%), 1 IDH mutant oligodendroglioma (1.4%), and 1 high-grade astrocytoma with piloid features (1.4%). 53/72 (73.6%) were primary and 19/72 (26.4%) were secondary GC. We used 40 patients without the GC pattern as controls. Among glioblastoma GC cases and in comparison with controls, mutations in PTEN and EGFR were significantly associated with the GC pattern: 18/57 (32%) vs 3/38 (7.9%), p-value=0.01 and 23/57 (40%) vs 6/38 (16%), p-value=0.013, respectively. This held true in primary but not secondary GC. Out of 20 most commonly mutated genes in GC, mutations in EGFR, TERT, and MDM4 were associated with worse PFS: p-value=0.004, p-value=0.007, p-value=0.013, respectively and mutations in TERT and MDM4, but not EGFR, were associated with worse OS: p-value=0.003, p-value=0.015, respectively. Secondary GC was associated with IDH mutation compared to control non-GC cases: 8/19 (42%) vs 2/40 (5%), p-value=0.001. As expected, IDH mutation was associated with improved PFS, p-value<0.001 and OS, p-value=0.003 in GC. No genes were significantly associated with laterality of GC. We found novel associations between PTEN and EGFR mutations and the GC phenotype and IDH mutation with the occurrence of secondary GC after treatment. While MDM4 is not associated with outcomes in gliomas, we show that MDM4 mutation is associated with poor survival in GC. These findings shed light into molecular basis of GC and need to be further validated in larger studies.