ID1 and breast cancer: Consistent with our previous finding that Id1 activates the Wnt/β-catenin/TCF pathway in human breast cancer [11], treatment with FH535, a small-molecule inhibitor of Wnt/β-catenin, repressed Id1-mediated c-Myc expression in MECs from MMTV-Id1 mice as confirmed by western blot and RT-PCR analysis (Figure 5C).