Typically, 5–30 PML-NBs are present in most mammalian cells nuclei, depending on the cell type and the cell cycle phase, while PML-NBs are disrupted and dispersed in microspeckles in the leukemic blasts of APL patients (Daniel et al., 1993; Dyck et al., 1994). The gene discussed is PML; the disease is acute promyelocytic leukemia.