Furthermore, p16INK4a-deficient human diploid fibroblasts and melanocytes, isolated from melanoma-prone individuals with inactivating mutations affecting both INK4a alleles, undergo delayed senescence (Sviderskaya etal., 2003; Brookes etal., 2004; Jones etal., 2007) and are readily immortalized by the introduction of the telomerase reverse transcriptase (Sviderskaya etal., 2003). This evidence concerns the gene CDKN2A and melanoma.