Chromosomal and immune dysregulation underlying granular mitosis in glioblastoma.

Abstract

Granular mitosis (GM) is a distinctive form of atypical mitosis characterized by dispersed chromosomal granules within the mitotic figure. Although described morphologically in glioblastoma, its molecular etiology has remained unknown. Data from The Cancer Genome Atlas (TCGA) Glioblastoma Multiforme cohort was analyzed. AI-assisted digital pathology was used to annotate mitotic figures, including GM, on hematoxylin and eosin-stained whole-slide images. Corresponding transcriptomic and genomic data were subjected to differential gene expression and copy number variation (CNV) analyses, followed by overrepresentation testing to identify enriched biological pathways. Clinical data were correlated to assess associations with molecular and pathological findings. Validation was performed on an independent glioblastoma cohort using immunohistochemistry. Sixty-three glioblastoma cases were included (32 GM-positive, 31 GM-negative). Transcriptomic analysis identified 185 differentially expressed genes (FDR <0.05; log₂FC >1.5). GM-positive tumors demonstrated broad downregulation of genes involved in nucleosome assembly, protein-DNA complex organization, and centromeric differentiation, alongside significant suppression of PI3K-Akt signaling (p = 5.58 × 10^-5). Unexpectedly, immune-related pathways-including Neutrophil extracellular trap (NET) formation and Cytokine-cytokine receptor interaction-were similarly underexpressed, indicating global suppression of innate immune signaling in GM-positive glioblastomas. Two CNVs were associated with a higher proportion of GM, demonstrating chromosomal fragility. Immunohistochemistry revealed a significantly higher density of immune cells, particularly macrophages and antigen-presenting cells, in close proximity to granular mitoses. Spatial correlation analysis demonstrated positive correlations between GM distribution and immune cell density across tumor regions. This study provides the first comprehensive molecular characterization of granular mitosis in glioblastoma. The findings link GM morphology to chromosomal disorganization, PI3K/PTEN pathway alterations, and impaired innate immunity, suggesting that GM represents a histologic correlate of centromeric stress and immune impairment in glioblastomas. Notably, granular mitoses are associated with localized immune cell enrichment and exhibit a positive spatial correlation with immune cell density within their microenvironment.