PATH-28. Molecular profiling of diffuse gliomas from a Brazilian private oncology network: the Oncoclínicas experience

Abstract Recent advances in molecular diagnostics have significantly reshaped glioma classification and prognostication. In addition, new predictive biomarkers for targeted agents and immunotherapies have increased the routine application of broad next-generation sequencing (NGS) in clinical practice. In this study, we analyzed a cohort of 138 adult patients with diffuse gliomas who underwent NGS panel testing targeting both DNA and RNA (Archer platform) at the OC Precision Medicine Laboratory. This approach enabled integrated molecular classification with two primary objectives: (1) to reclassify tumor grade based on molecular criteria and (2) to identify potentially actionable driver alterations. Of the 138 diffuse glioma cases included, 43 (31%) were initially classified as WHO grade 2 or 3. Among these, 15 (35%) were IDH-wildtype. Of these, five were upgraded to grade 4 based on diagnostic molecular alterations consistent with glioblastoma IDH-wildtype and diffuse hemispheric glioma. One additional IDH-mutant tumor with homozygous deletion of CDKN2A/B was also reclassified as grade 4. In total, six tumors (14%) were reclassified based on molecular features. The most frequent IDH1 variant was R132H (82%), followed by R132C (7%), R132S (4%), and IDH2 R172K and R172W (4% each). Among grade 4 gliomas in patients under 55, common alterations included TP53 (70%), ATRX (50%), IDH1 (20%), NF1 (20%), PTEN (5%), and EGFR (5%). In contrast, high-grade gliomas in patients ≥55 years showed higher frequencies of EGFR (43%), TERT (48%), PTEN (33%), TP53 (22%), CDKN2A (14%), CDKN2B (2%), and NF1 (16%). Actionable alterations beyond IDH1/2 were identified, including four BRAF V600E mutations (3%) and two ultramutated tumors with high tumor mutational burden (TMB), one with microsatellite instability (MSI). Overall survival data were available in five patients reclassified to grade 4 (median OS: 9.8 months) and 14 grade 2/3 patients (median not reached, 60% alive at 2 years). These findings underscore the molecular heterogeneity of diffuse gliomas and reinforce the importance of integrated molecular diagnostics in guiding clinical management.