A 4-miRNA signature predicts the therapeutic outcome of glioblastoma.

Background: Inter-individual variability in terms of treatment outcome and benefit from standard of care treatment is a great challenge in the multimodal therapy of glioblastoma (GBM). In order to recognize patients with particularly poor prognosis a priori and assigning them to alternative treatment approaches, molecular signatures predicting outcome with higher accuracy would be helpful. In our study, we  examined whether such a signature can be defined on the basis of miRNA expression analyses. Methods: FFPE sections of resected tumours from 36 standard-of-care treated GBM patients along with overall survival follow-up data were collected retrospectively and subjected to lowcomplexity signature identification from miRNA microarray data. Based on the expression of the signature miRNAs and cox-proportional hazard coefficients, a risk score was calculated and used for classification into higher- and lower-risk patients. The identified signature was validated in a miRNA array data set of a subset of the TCGA GBM cohort which was matched for sex, age and treatment. In order to assess the functional impact, genes putatively regulated by the signature miRNAs were identified by correlation with global transcriptome data, followed by pathway analysis. Results: We identified a prognostic 4-miRNA signature that was independent of MGMT promoter methylation status, age, and sex. A risk score was assigned to each patient that allowed defining two groups significantly differing in prognosis (p-value: 0.0001, median survival: 10.6 months and 15.1 months, hazard ratio = 3.8). The signature was technically validated by qRT-PCR and independently validated in an age- and sex-matched subset of standard-of-care treated patients of the TCGA GBM cohort (n=58). Pathway analysis suggested tumorigenesis-associated processes such as immune response, extracellular matrix organization, axon guidance, signalling by NGF, GPCR and Wnt. Conclusions: In the present study, we describe the identification and independent validation of a 4-miRNA signature that allows stratification of GBM patients into different prognostic groups in combination with one defined threshold and set of coefficients. This miRNA signature could be utilized as diagnostic tool for the identification of GBM patients for improved and/or alternative treatment approaches