The present invention relates the treatment and prognostic of cancer like glioblastoma. Here, the inventors focused their study on the impact of presence of N6-adenosine methylation in miRNA-200b-3p in samples of patients suffering from glioblastoma multiforme (GBM). Their study was particularly focused on the impact of miRNA-200b-3p and its adenosine methylation on the expression of XIAP. XIAP acts as an anti-apoptotic protein via the inhibition of caspase-3 and -7 activation and high XIAP expression is associated with a poor survival in several solid tumors. Thus, the miR-200b-3p-mediated repression of XIAP mRNA expression appears as a mechanism governing the caspase-3 and -7 activity and the apoptosis. In theory, in the presence of miR-200b-3p, XIAP mRNA expression is repressed and caspase-3 and -7 can be activated to promote apoptosis. Thus, the present invention relates to an in vitro method for determining the prognosis of the survival time of a patient suffering from a cancer comprising the steps consisting of i) determining the expression level of the miR-200b-3p and/or the N6-adenosine methylated miRNA-200b-3p (miR-200b-3p m6A) in a sample from said patient and to the N6-adenosine methylated miRNA-200b-3p (miR-200b-3p m6A) for use in the treatment of a cancer in a subject in need thereof.