In contrast to the role in ER− breast cancer (basal-like and ErbB2+) summarized above, CD151 appears to be tumor suppressive in some cases, for example, during the development and growth of ER+ mammary tumors in the mouse mammary tumor virus (MMTV) promoter-driven Wnt1 oncogene model (Figure 2B) [28]. This evidence concerns the gene WNT1 and breast cancer.