P18.26.A IMPROVED OUTCOME PREDICTION AND GRADING OF THE NOVEL TUMOUR TYPE GLIOMATOSIS CEREBRI-LIKE GLIOMA, IDH-WILDTYPE (GCLG, IDH-WT)

Abstract BACKGROUND Based on a cohort of 16 patients, we recently described a novel tumour type of IDH-wildtype glioma in adult patients, characterised by a gliomatosis cerebri-like growth pattern, frequent TERT promoter mutations, and a distinct epigenetic profile (GCLG, IDH-wildtype; DKFZ brain tumour classifier: adult-type high grade glioma, subtype F, HGG-F). MATERIAL AND METHODS We now compiled a larger, multicentric series of 63 patients and conducted an in-depth morphological, molecular and clinical characterisation. RESULTS The series consisted of 43 male and 15 female (NA = 5) patients. Median age was 65 years (range 17-88 years). In the initial series, none of the cases demonstrated vascular proliferation or necrosis; in contrast, 6/50 cases in this extended cohort (12%) showed histological features of malignancy (i.e. vascular proliferation and/or necrosis). In addition, 40% demonstrated molecular features of high-grade gliomas (i.e., CDKN2A/B homozygous deletion, chr.+7/-10, high-level amplifications of EGFR, CDK4, PDGFRA). Progression-free and overall survival in GCLG with and without histological and/or molecular signs of malignancy were significantly different (p