However, as serum levels of IL-6 are elevated in Δ122p53/mΔpro mice compared with other genotypes (Figure 1c), and IL-6 is a marker of the so-called senescence associated secretory phenotype,36 we looked for evidence of senescent cells in the tumor sections from the mice by immunostaining for the senescence marker p16INK4A. Here, CDKN2A is linked to neoplasm.