MicroRNAs as Multifaceted Players in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common and inevitably lethal primary brain tumor, with a median survival rate of only 15 months from diagnosis. The current standard treatment involves maximal surgical resection flanked by radiotherapy and chemotherapy with the alkylating agent temozolomide. However, even such aggressive treatment is never curative, and recurrent tumors always arise, commonly in more aggressive, chemo- and radio-resistant forms, leading to untreatable and deadly tumors. MicroRNAs, recognized major players in cancer, are deeply involved in GBM, as shown by more than a decade of studies. In this review, we revise the main milestones of MicroRNA studies in GBM, and the latest relevant discoveries in this field. Examples are given of MicroRNAs working as "oncomiRs" or tumor suppressors, with specific connections with GBM clinical subtypes, patients' survival, and resistance to therapies. As the interaction of GBM cells with the microenvironment was proven as a key determinant of tumor growth, the role of MicroRNAs in GBM microenvironment, tumor angiogenesis, and tumor-secreted microvesicles is also reviewed. Finally, we discuss the latest findings presenting MicroRNAs as possible therapeutic targets for GBM, or their use as circulating biomarkers in diagnosis and prognosis.