TP53 and cancer: While wt p53 expression remains intact in around 50% of all cancers, it is often suppressed by dysfunctional activation pathways, for example epigenetic silencing of p14 ARF expression or overexpression of negative feedback regulators such as murine double-minute 2 (MDM2) and its structural homolog, murine double-minute X (MDMX) (19, 20).