Chromosomal instability is associated with paradoxical cGAS upregulation and impaired STING signaling shaping the immune microenvironment in glioblastoma.

Glioblastoma (GBM) is characterized by pronounced chromosomal instability (CIN), which can activate the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway and promote anti-tumor immunity. How CIN engages cGAS-STING in immunologically "cold" GBM and its relation to clinical outcomes remain unclear. CIN was quantified in 74 tissue cores from 34 patients with isocitrate dehydrogenase-wildtype GBM by chromosome 7/10 fluorescence in situ hybridization; aneuploidy score (AS) and heterogeneity score were derived. Immunohistochemistry assessed cGAS, STING, phosphorylated IRF3 (p-IRF3), and immune markers (CD3, CD4, CD8, CD163, IBA-1). Polyploid giant cancer cells (PGCCs) were identified using hematoxylin and eosin staining. EGFR, PDGFRA, CDKN2A, and PTEN copy-number alterations were assessed by multiplex ligation-dependent probe amplification. The Cancer Genome Atlas (TCGA)-GBM cohort served as an independent dataset. High AS (≥1.36) was associated with longer overall survival (22.7 vs. 16.0 months, P = .039). cGAS expression correlated positively with AS (P = .019), consistent with cGAS engagement in highly aneuploid tumors. Conversely, STING was rarely expressed in tumor cells, restricted to stromal and vascular compartments, without accompanying immune infiltration. STING-positive regions were enriched for PGCCs (P = .045), suggesting stress adaptation rather than immune activation. p-IRF3 modestly correlated with AS (Spearman r = 0.39, P = .0006) and was reduced in EGFR-amplified or PTEN-loss cores (P = .003 each). In TCGA-GBM, surrogate AS stratification revealed a biphasic survival pattern consistent with our findings. CIN was associated with cGAS upregulation but not functional STING-mediated immunity in GBM, suggesting that CIN-associated intrinsic stress adaptation may contribute to immunotherapy resistance in GBM.