XAF1 and cancer: Given that both XAF1 and IRF-1 are frequently inactivated in multiple human cancers, it is conceivable that disruption of the XAF1−IRF-1 axis by loss of expression of XAF1 or IRF-1, isoform switch of XAF1 transcript, or oncogenic activation of Ras/MEK signaling might be a common event that drives tumorigenesis.