CDKN2A and neoplasm: Several biomarkers have been used for quantitative assessment of cell senescence, including senescence-associated β-galactosidase (SA-β gal) and the cyclin-dependent kinase inhibitors, p16INK4A and p21WAF1, that are involved in the control of growth arrest by two major tumour suppressor pathways, p16INK4A/pRb and p53/p21WAF1 [25,26].