PTEN and glioblastoma: The most common genetic alterations identified in GBM patients by The Cancer Genome Atlas project are related to the overactivation of the receptor tyrosine kinase (RTK)/Ras/phosphatidylinositol 3-kinase (PI3K) pathway (88% of all cases), gained by the mutation/amplification of RTKs and PI3K, or loss of function of PTEN (phosphatase and tensin homolog), a phosphatase that counteracts action of PI3K.