Cellular senescence refers to the response of cells to a variety of stimuli, many of which have the potential to induce preneoplastic or neoplastic phenotypes. These stimuli include dysfunctional telomeres, DNA damage, disrupted chromatin structures, the expression of certain oncogenes, and supraphysiologic mitogenic signals. The most prominent outcome of the senescence response is an essentially irreversible arrest of cell proliferation. In addition, senescent cells acquire marked changes in cell morphology and function. In some cases, senescent cells also acquire resistance to certain signals that induce apoptotic cell death (1 –4 ).
