CDKN1A and neoplasm: Senescence is a cellular phenotype, initially described in cell culture, that is acquired in a variety of normal and tumor-derived cells following activation of the p53/p21Cip1/Waf1-, Rb/p16Ink4a-dependent DNA damage response and characterized by irreversible proliferation arrest coupled with a constitutive pro-inflammatory secretory phenotype (SASP) [1–3].