NUMB and breast cancer: The PCR results indicated that both the β-catenin and RAC1 could bind to the promoter region of NUMB in breast cancer cells, whereas RAC1 binding to the NUMB promoter region was substantially weaker in colon cancer HCT116 cells; however, very strong interaction between β-catenin and the NUMB promoter region were detected in HCT116 cells (Figure 5d(ii)).