BMI1 and breast cancer: Bmi-1 is also needed for the maintenance and self-renewal of cancer stem-like cells/tumor-initiating cells in leukemia [9–11], colorectal cancer [12], liver cancer [13], glioma [14, 15], breast cancer [16, 17], prostate cancer [18, 19], head and neck squamous cell carcinoma [20], and medulloblastoma [21].