MDM4 and neoplasm: The p53 tumor suppressor network is frequently disrupted in GBM, and the deregulation of p53 antagonists, such as MDM2 and MDM4 (also known as HDMX and MDMX), is a primary contributor to p53 inactivation in this context.24 The MDM2 proteins are dysregulated in many human cancers, and they exert their oncogenic activity predominantly by inhibiting the activity of p53.