As reported previously18 and shown in Figure 4B, high expression of p19Arf in RUNX2/MYC/p53+/− lymphoma lines that rapidly lose the wild‐type allele and p53 protein expression on establishment in vitro argues strongly that aberrant in vivo activity is not because of direct mutation of either p19Arf or p53. The gene discussed is TP53; the disease is lymphoma.