Cystic glioblastoma IDH-wildtype: genetic alterations and outcomes.

Purpose: In the past decade, studies have reclassified infiltrating glioblastomas (GBM) IDH-wildtype utilizing molecular and phenotypic features. Cystic GBMs are one such phenotypic subtype whose genetic and clinical characteristics remain incompletely understood. The goal of this study was to genetically characterize cystic GBMs and examine patient outcomes as compared to non-cystic GBMs.

Methods: Retrospective analysis of GBM IDH-wildtype with pre-operative and post-operative MRI and comprehensive next-generation sequencing were performed with evaluation of 205 genes. Tumors were evaluated by their cystic characteristics. Benjamini-Hochberg's false discovery rate (BH-FDR) was performed for multiple comparison adjustments. Univariable and multivariable analysis for survival was performed.

Results: 176 GBM IDH-WT patients met the inclusion criteria. Of these, 17 patients were identified as having a cystic component. Compared to non-cystic GBMs, cystic GBMs had a higher incidence of mutation in PDGFRA (41.2% vs. 16.4%, p = 0.021), RB1 (35.3% vs 11.9%, p = 0.019), and KIT (35.3% vs 10.7%, p = 0.012), and a lower incidence of mutation in CDKN2A/B (41.2% vs 69.2%, p = 0.029). No difference in progression-free survival (6.87 vs 7.83 months. p = 0.541) or overall survival (19.5 vs 18.2 months, p = 0.243) was identified between patients with cystic versus non-cystic GBM.

Conclusions: Cystic GBMs were found to have lower frequencies of CDKN2A/B alterations and higher frequencies of PDGFRA, KIT, and RB1 alterations as compared to non-cystic GBMs. No statistically significant differences in PFS or OS were identified.