Inside and out: the activities of senescence in cancer

Recent advances in understanding the biology of senescent cells, especially the secretory phenotypes and the role of immune cell clearance of senescent cells, has revealed more about the role of senescence induction in tumorigenesis and tumour progression. This includes the surprising findings that senescence may promote tumour growth in some contexts. The core aspect of the senescent phenotype is a stable state of cell cycle arrest. However, this is a disguise that conceals a highly active metabolic cell state with diverse functionality. Both the cell-autonomous and the non-cell-autonomous activities of senescent cells create spatiotemporally dynamic and context-dependent tissue reactions. For example, the senescence-associated secretory phenotype (SASP) provokes not only tumour-suppressive but also tumour-promoting responses. Senescence is now increasingly considered to be an integrated and widespread component that is potentially important for tumour development, tumour suppression and the response to therapy.