DKK1 and cancer: Factors involved in the maintenance of stem and cancer cell quiescence, such as Bmp4, Bmp6, Bmp7, Kit ligand, TGF-β2, Dkk-1, Dkk3 and thombospondin2 (Thbs2), are higher in the bones of young mice than in old mice, but radiation markedly upregulates them in old mice [97].