“…Numerous studies reported since the 1990s, some from our laboratory [ 53 , 54 , 55 , 56 , 57 ], have established the presence of a threshold mechanism for stress-induced growth arrest versus apoptosis in human cells with different p53 status, with moderate doses of DNA-damaging agents predominantly (if not solely) triggering growth arrest (e.g., SIPS) in some cell types. This threshold effect has been observed for ionizing radiation [ 54 , 55 , 56 , 57 , 58 , 59 ], 254 nm ultraviolet light (UV) [ 53 , 54 , 60 , 61 ] and chemotherapeutic agents [ 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ].…”