Extremely low or undetectable Xaf1 expression is a frequent event in several cancer cell lines,25 as well as in human cancer tissues.26, 27 The restoration of Xaf1 expression induced cancer cell apoptosis, cell cycle arrest and inhibited tumor growth in various types of cancers, as well as resulting in an increased cell sensitivity to drug-induced apoptosis. The gene discussed is XAF1; the disease is cancer.