PML and cancer: It has been observed in a number of studies that PML expression is completely or substantially lost, via unknown mechanisms, in many tumor types that are not known to be ATRX-deficient (Zhang et al., 2000b; Gurrieri et al., 2004; Lee et al., 2007; Reineke et al., 2008), and a more extensive survey of PML expression in cancer could potentially reveal many more.