The standard SA-beta-gal staining, while indicative of the presence of senescent cells, is not an absolute marker for senescent cell and indicates increased lysosmal b-galactosidase activity. The use of several molecular markers that represent different characteristics of senescent cells is necessary (see figure). Such molecular markers can represent the cell cycle arrest machinery (e.g. p53, p21, p16), lack of cellular proliferation (e.g. lack of BrdU incorporation, Ki67), activation of the DDR (e.g. gamamH2AX or p53BP1 foci), expression of secretory factors (e.g. IL-6 and IL-8), the activation of the pathways that regulate the secretory phenotype (e.g. p-p65 or p-p38), the activation of immune surveillance-related genes and possible regulators for their pro-survival response (DCR2, p-Akt, p-Erk).