1. Mechanistically, many chemotherapies cause DNA damage in cancer cells, which triggers senescence through ATM–CHK2 and ATR–CHK1 kinase-mediated activation of the interconnected p53–RB pathways.2. Radiotherapy can induce an irreparable DNA damage response that activates ATM or ATR and p53–p21 pathway-mediated apoptosis and cellular senescence.3. SASP cytokines, chemokines and other factors that modulate immune cells can either promote or inhibit senescent cell clearance. This evidence concerns the gene CHEK2 and cancer.