Also, the strong expression of BMI1 can occur in CLL but is not necessarily connected to high proliferative activity, as we detected a continuum of BMI1 expression in the low proliferating group of CLL (Fig. 6, B to D) just as a TP53 loss alone did not necessarily lead to a more aggressive behavior of the CLL. The gene discussed is BMI1; the disease is B-cell chronic lymphocytic leukemia.