BMI1 and cancer: B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is a polycomb group protein that regulates cell proliferation and has been found to be upregulated in a variety of human cancer types, including acute myeloid leukemia and breast, colon, lung, ovarian and nasopharyngeal cancer; this suggests a potential role of Bmi-1 as an oncogene (9–12).