For example, ARF can induce cell growth arrest in tumour cells that lack a functional p53 gene or its key transcriptional target p21 (Weber et al, 2000; Modestou et al, 2001; Korgaonkar et al, 2002; Eymin et al, 2003; Normand et al, 2005). This evidence concerns the gene TP53 and neoplasm.