Specifically, p21-null animals develop tumors at an average age of 16 months and with reduced incidence (27% in females, 55% in males) compared to mice lacking p53. Thus, a milder tumor phenotype for NIAMm/m mice is not surprising since it represents just one of many p53 regulators [1], [3]. The gene discussed is CDKN1A; the disease is neoplasm.