In particular, Bmi-1 overexpression is detected in several types of human cancers (Bea et al, 2001; Kim et al, 2004a, 2004b; Breuer et al, 2005), leading to the hypothesis that Bmi-1 facilitates tumorigenesis by nullifying the p16INK4A-mediated extrinsic senescence pathway. This evidence concerns the gene BMI1 and cancer.