To determine what types of cells in the Wnt1 tumors express SDF1, we injected dissociated Wnt1 tumor cells into the mammary fat pads of immune-deficient Rag2−/−mice constitutively expressing an enhanced green fluorescent protein under control of the chicken β-actin promoter (EGFPtg/Rag2−/−). Here, WNT1 is linked to neoplasm.