We previously evaluated the role of Lrp5 and Lrp6 in a mammary tumor model in which the ectopic expression of Wnt1 under the control of the MMTV promoter (MMTV-Wnt1) causes the rapid onset of mammary tumors (Lindvall et al., 2006, 2009; Badders et al., 2009). Here, LRP5 is linked to breast cancer.