IL6 and neoplasm: 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.