H2AX and acute promyelocytic leukemia: Double immunofluorescence staining with anti-PML and anti-γ-H2AX antibodies allowed the detection of disassembled PML-NBs and high number of γ-H2AX foci in primary blasts isolated at diagnosis from three APL patients, harboring the chromosomal translocation t(15;17) resulting in the PML-RARα fusion product (also confirmed by RT-PCR, Figures 1a and b).