CRK and glioblastoma: Moreover, the fact that Crk Tyr251 can also be phosphorylated by EGFR [38] indicates that the Tyr251 Crk/Abl axis might be particularly relevant in classical GBM, as EGFR gene amplification and overexpression is a particularly striking feature of this tumor type, which is among the most aggressive and invasive forms of this cancer.