BIOM-01. <i>CDKN2A</i> HOMOZYGOUS DELETION HAS STRONGER PROGNOSTIC POWER THAN<i>IDH</i> MUTATION IN CNS WHO GRADE 4 GLIOMAS

Abstract We conducted retrospective analysis of glioma cohorts in our institute. Medical records were reviewed for 142 glioblastoma patients for 15 years, and pathological slides were examined again for the updated diagnosis according to 2021 WHO classification of CNS tumors. The IDH mutation and CDKN2A deletion were examined by NGS analysis using ONCOaccuPanel®. Traditional prognostic factors were also examined. Mean follow-up duration was 27.5 months (ranged from 4.1 to 43.5 months) and mean overall survival (OS) was 19.4 months (95% CI 16.3 – 20.9 months). After the exclusion of 4 patients with poor status of pathologic samples, total 109 glioblastoma which were diagnosed by previous WHO criteria were changed into 26 (23.9%) astrocytoma, IDH-mutant, CNS WHO grade 4 and 83 (76.1%) glioblastoma, IDH-wildtype, CNS WHO grade 4. Among them, 61 patients (56.0%) had CDKN2A deletion. Group A was classified for 59 patients with IDH-wildtype and present CDKN2A deletion, group B was classified for 16 patients with IDH-mutant and present CDKN2A deletion, group C was classified for 48 patients with IDH-wildtype and absent CDKN2A deletion, and group D was classified for 13 patients with IDH-mutant and absent CDKN2A deletion. Group A had a mean OS of 15.70 months (95% CI 13.86 – 17.54 months), group B had a mean OS of 19.37 months (95% CI 13.43 – 25.30 months), group C had a mean OS of 22.63 months (95% CI 20.10 – 25.17 months), and group D had a mean OS of 33.38 months (95% CI 29.35 – 37.40 months). Multivariate analysis showed IDH mutation (mutant vs. wildtype; HR 6.358), and CDKN2A deletion (absence vs. presence; HR 13.452). The presenting study suggest that CDKN2A deletion should play a powerful prognostic role in CNS WHO grade 4 gliomas as well as low grade glioma. Even if CNS WHO grade 4 gliomas had mutant IDH, they can have poor clinical outcome due to CDKN2A deletion.