Potential Association of BRAF and PIK3CA Copy Number Alterations with Long-Term Survival in IDH-Wildtype...

IDH-wildtype glioblastoma remains the most aggressive primary brain tumor, with a median overall survival (OS) of 14-16 months despite maximal treatment. A small subset of patients, however, survive beyond 30 months, suggesting distinct underlying biological features. The aim of this pilot study was to explore whether selected molecular alterations detectable by FISH show differing distribution patterns between patients with prolonged and poor survival in IDH-wildtype glioblastoma. We retrospectively analyzed 20 patients with newly diagnosed primary IDH-wildtype glioblastoma who underwent gross-total resection followed by standard radiotherapy and temozolomide treatment between 2016 and 2022. Patients were categorized into two predefined groups according to survival outcomes: long-term survivors (OS > 30 months) and short-term survivors (OS < 10 months). Fluorescence in situ hybridization (FISH) was used to evaluate alterations in ATRX, BRAF, and PIK3CA. MGMT promoter methylation, EGFR amplification, and TERT promoter mutation status were obtained from routine diagnostic reports. Because survival groups were intentionally pre-selected as extreme phenotypes, time-to-event analysis was not appropriate. Therefore, statistical comparisons were performed using Fisher's exact test and multivariable logistic regression with long-term versus short-term survival as a binary outcome. Short-term survivors had a significantly higher median age (57.5 vs. 46.5 years, p = 0.043) and a higher rate of EGFR amplification (100% vs. 50%, p = 0.033). Strikingly, combined BRAF and PIK3CA alterations (predominantly polysomy) were detected in 8 out of 10 (80%) long-term survivors, compared to 0 out of 10 (0%) short-term survivors (p = 0.0007). In multivariable logistic regression adjusted for age and MGMT promoter methylation, BRAF/PIK3CA alteration remained strongly associated with long-term survival, though the effect size was mathematically inflated due to perfect separation (0 events in Group B). BRAF and PIK3CA copy number alterations were observed exclusively in long-term survivors in this small exploratory cohort, suggesting a possible association with prolonged survival. However, given the limited sample size, the selection of extreme survival groups, and the predominance of chromosomal polysomy detected by FISH, these findings should be interpreted as hypothesis-generating only. Further validation in larger cohorts using high-resolution genomic methods is warranted.