TP53 and glioblastoma: Furthermore, deregulation of oncogenes or tumor suppressors may modulate Notch signaling in a downstream way, as lack or inhibition of the negative regulator of NIC Numb has been linked to enhanced activity of Notch in breast cancer, glioblastoma multiforme (GBM), and NSCLC [83,96,97], while inactivation of p53 has been demonstrated to lead to up- or downregulation of Notch signaling in several cancers (reviewed in [98]).