Targeted DNA Sequencing Reveals Molecular Factors Associated with Clinical Outcomes in Recurrent Glioblastoma

INTRODUCTION: The prognostic significance of molecular alterations in recurrent glioblastoma (rGBM) remains unclear. METHODS: 121 consecutive glioblastoma (GBM) patients who underwent re-resection at a single institution from 2016-2021 were retrospectively reviewed. All patients underwent maximal safe resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ) at time of initial diagnosis. DNA mutations from re-resection samples were assessed with a CLIA certified next-generation targeted DNA sequencing assay. Overall (OS) and progression-free survival (PFS) from re-resection were analyzed with the Kaplan-Meier method and Cox regression analyses. RESULTS: Median age at first recurrence was 57 years (range, 27-78), and median follow up from re-resection was 11 months. Salvage therapy comprised re-irradiation (n = 52, 43%), temozolomide (TMZ) (n = 39, 32%), lomustine (n = 47, 39%), and/or bevacizumab (n = 22, 18%). Median OS and PFS times were 12.1 and 4.4 months, respectively. Median tumor mutation burden (TMB) was 4 mut/Mb (range, 1-650), microsatellite instability (MSI) was 1.16% (range, 0-20), and MGMT methylation was present in 71 (59%) patients. Longer OS was found after postoperative TMZ (19.1 vs. 9.1), KPS >70 (13.6 vs. 11.1), and/or re-irradiation (12.6 vs. 8.4) (p < .05 for each). On multivariate analysis, TMZ (HR 0.2, 0.079-0.48), re-irradiation (HR 0.27, 0.12-0.58), and mutations in the PDGFRA (HR 0.24, 0.067-0.83) or PTEN (HR 2.3, 1.1-4.8) genes on targeted sequencing were associated with longer OS after re-resection (p < .05). Multivariate predictors of re-irradiation response included MSI > 1.16 (HR 0.25, 0.084-0.75), and mutations in PDGFRA (HR 0.04, 0.005-0.33), TERT (HR 0.16, 0.033-0.78), or PIK3R1 (HR 0.18, 0.041-0.8) genes. In the 46 matched primary/recurrent tumors, 40 (46%) had a longitudinal change in a mutation and 9 (24%) demonstrated hypermutation, of which 4 (57%) had simultaneous mismatch repair deficiencies. CONCLUSIONS: Our study identifies molecular factors associated with survival and response to re-irradiation in rGBM.