Management for Different Glioma Subtypes: Are All Low-Grade Gliomas Created Equal?

The Emerging Role of Extracellular Vesicles in the Glioma Microenvironment: Biogenesis and Clinical Relevance

Gliomas are a diverse group of brain tumors comprised of malignant cells ('tumor' cells) and non-malignant 'normal' cells, including neural (neurons, glia), inflammatory (microglia, macrophage) and vascular cells. Tumor heterogeneity arises in part because, within the glioma mass, both 'tumor' and 'normal' cells secrete factors that form a unique microenvironment to influence tumor progression. Extracellular vesicles (EVs) are critical mediators of intercellular communication between immediate cellular neighbors and distantly located cells in healthy tissues/organs and in tumors, including gliomas. EVs mediate cell-cell signaling as carriers of nucleic acid, lipid and protein cargo, and their content is unique to cell types and physiological states. EVs secreted by non-malignant neural cells have important physiological roles in the healthy brain, which can be altered or co-opted to promote tumor progression and metastasis, acting in combination with glioma-secreted EVs. The cell-type specificity of EV content means that 'vesiculome' data can potentially be used to trace the cell of origin. EVs may also serve as biomarkers to be exploited for disease diagnosis and to assess therapeutic progress. In this review, we discuss how EVs mediate intercellular communication in glioma, and their potential role as biomarkers and readouts of a therapeutic response.

FGFR- gene family alterations in low-grade neuroepithelial tumors

The discovery of fibroblast growth factor receptor (FGFR) gene family alterations as drivers of primary brain tumors has generated significant excitement, both as potential therapeutic targets as well as defining hallmarks of histologic entities. However, FGFR alterations among neuroepithelial lesions are not restricted to high or low grade, nor to adult vs. pediatric-type tumors. While it may be tempting to consider FGFR-altered tumors as a unified group, this underlying heterogeneity poses diagnostic and interpretive challenges. Therefore, understanding the underlying biology of tumors harboring specific FGFR alterations is critical. In this review, recent evidence for recurrent FGFR alterations in histologically and biologically low-grade neuroepithelial tumors (LGNTs) is examined (namely FGFR1 tyrosine kinase domain duplication in low grade glioma, FGFR1-TACC1 fusions in extraventricular neurocytoma [EVN], and FGFR2-CTNNA3 fusions in polymorphous low-grade neuroepithelial tumor of the young [PLNTY]). Additionally, FGFR alterations with less well-defined prognostic implications are considered (FGFR3-TACC3 fusions, FGFR1 hotspot mutations). Finally, a framework for practical interpretation of FGFR alterations in low grade glial/glioneuronal tumors is proposed.

FGFR- gene family alterations in low-grade neuroepithelial tumors

The discovery of fibroblast growth factor receptor (FGFR) gene family alterations as drivers of primary brain tumors has generated significant excitement, both as potential therapeutic targets as well as defining hallmarks of histologic entities. However, FGFR alterations among neuroepithelial lesions are not restricted to high or low grade, nor to adult vs. pediatric-type tumors. While it may be tempting to consider FGFR-altered tumors as a unified group, this underlying heterogeneity poses diagnostic and interpretive challenges. Therefore, understanding the underlying biology of tumors harboring specific FGFR alterations is critical. In this review, recent evidence for recurrent FGFR alterations in histologically and biologically low-grade neuroepithelial tumors (LGNTs) is examined (namely FGFR1 tyrosine kinase domain duplication in low grade glioma, FGFR1-TACC1 fusions in extraventricular neurocytoma [EVN], and FGFR2-CTNNA3 fusions in polymorphous low-grade neuroepithelial tumor of the young [PLNTY]). Additionally, FGFR alterations with less well-defined prognostic implications are considered (FGFR3-TACC3 fusions, FGFR1 hotspot mutations). Finally, a framework for practical interpretation of FGFR alterations in low grade glial/glioneuronal tumors is proposed.