At this point, it must be mentioned that a variety of tumor cells have been found with increased numbers of γH2AX foci suggesting to be related to the overall chromosomal instability of these cells . Last but not least, it has been also indicated by Banath et al. that persistence of DNA damage-induced γH2AX foci can be suggestive of lethal DNA damage so that it may be possible to predict tumor cell killing by different DNA damaging therapeutic agents by measuring the fraction of cells that retain γH2AX signalling .