Mouse models of childhood cancer of the nervous system.M A Dyer. J Clin Pathol 2004;57:561–76. The author apologises for the ambiguous sentence on page 573. The sentence: “Tumours form when Rb, p107, and p53 are inactivated, but whether p107, p53, or both genes must be inactivated for retinoblastoma to form in the mouse retina is unknown.” should have read: “Tumours form when Rb, p107, and p53 are inactivated, or when Rb and p107 are inactivated. However, it is not known whether p107, p53, or both genes must be inactivated for metastatic retinoblastoma to form in the mouse retina because all possible genetic combinations were not characterised.”