E2F1 activity, which activates tumor suppressor genes, is distinct from that which activates growth-related genes, in that E2F1, induced by growth stimulation, does not activate tumor suppressor genes [12,18,19] and, at least for the ARF gene, is not dependent on its heterodimeric partner DRTF polypeptide (DP) [46], which is strictly required for activation of growth-related E2F target genes [47,48]. This evidence concerns the gene CDKN2A and neoplasm.