For example, germ-line and conditional, Cre-mediated deletions of E2f3 in vivo intimate that E2F3 has unique roles not shared with other activator E2F family members4, 5 during embryonic development6, 7, in myogenic differentiation8, neuronal migration9, DNA damage responses10 and in some cancers such as HER2-driven mammary tumours11, 12, Ewing’s sarcoma and prostate cancer13. The gene discussed is E2F3; the disease is cancer.