Abstract 706: Beyond a single core biopsy: Spatial genomic profiling improves therapeutic target detection in glioblastoma.

Abstract Purpose: Despite advances in molecular diagnostics, glioblastoma (GBM) remains incurable, with recurrence driven by residual invasive tumor cells that escape surgical resection and therapy. Current genomic profiling to guide therapy for recurrent disease typically relies on a single-site clinical biopsy (SSCB) obtained from the contrasting-enhancing (CE) tumor core - the region targeted for maximal resection and most visible on Magnetic Resonance Imaging (MRI). However, this region poorly represents the non-enhancing (NE) invasive tumor margins, which harbor treatment-resistant and genetically distinct cell populations responsible for disease recurrence. GBM exhibits extensive spatial heterogeneity, raising concerns that a single tissue may underrepresent the true actionable landscape of the tumor. Experimental Procedures: We analyzed 302 biopsies from 66 GBM patients who underwent multiregional whole exome and RNA sequencing across CE and NE tumor regions. Of these, 17 patients also had standard-of-care SSCB molecular profiling utilizing clinically available genomic sequencing panels outside of the multiregional protocol. Variants that have been targeted in ongoing or successful human clinical trials were annotated as actionable. We compared actionability profiles between SSCB and multiregional sampling, to determine the gain of actionable variant detection across the two sampling strategies. We performed an in-silico biopsy simulation to model the coverage of these alterations across the tumor landscape with increasing sampling frequency in the multiregional protocol, versus the coverage from clinical sequencing panels on SSCBs. Results: Clinical sampling identified a median of one actionable mutation per patient (range 0-3). In contrast, multiregional profiling revealed additional potentially actionable variants in over 70% of patients, particularly within NE infiltrative regions that are not captured by conventional resection. Notably, nine potentially actionable copy-number variants, including PDGFRA amplification, were consistently absent from SSCB results and underrepresented in most clinical panels. In silico biopsy simulations demonstrated that actionable variant detection continues to rise even after sampling five additional regions, reflecting spatial segregation of therapeutic targets. Conclusions: These findings demonstrate that a single sample from the CE tumor core fails to capture the biologically diverse invasive tumor populations responsible for GBM recurrence. Multiregional sequencing uncovers clinically meaningful alterations that would otherwise remain undetected with conventional sampling, highlighting the risk of incomplete molecular characterization in current clinical biopsy workflows. Citation Format: Enmar Harfoush, Taylor Weiskittel, Mylan Blomquist, Dustin Grief, Aadel A. Chaudhuri, Leland S. Hu, Nhan L. Tran, Shannon Fortin-Ensign. Beyond a single core biopsy: Spatial genomic profiling improves therapeutic target detection in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 706.