ATM and cancer: The importance of our newly revealed mechanism is reflected by the fact that close to 50% of spontaneously arising DSBs are caused by sublethal caspase activation; (2) that spDSBs by themselves, irrespective of their effects on chromosomal aneuploidy and gene mutations, play a key role in driving tumorigenicity and stemness of cancer cells through persistent activation of ATM and DDR (Figure 9).