DNA damage is able to induce senescence in tumor cells in vitro and in vivo.

Often the use of cytotoxic drugs in cancer therapy results in stable disease rather than regression of the tumor, and this is typically seen as a failure of treatment. We now show that DNA damage is able to induce senescence in tumor cells expressing wild-type p53. We also show that cytotoxics are capable of inducing senescence in tumor tissue in vivo. Our results suggest that p53 and p21 play a central role in the onset of senescence, whereas p16(INK4a) function may be involved in maintaining senescence. Thus, like apoptosis, senescence appears to be a p53-induced cellular response to DNA damage and an important factor in determining treatment outcome.