RARA and acute promyelocytic leukemia: Interestingly, high levels of γ-H2AX foci were found in human tumors and cultured cells,39 during the S phase of the cell cycle, and during apoptosis.34 The cell cycle analysis in APL blasts and in PML-RARα-expressing cells seems to exclude the possibility that H2AX phosphorylation depends on the percentage of cells in the S phase or on apoptotic events.