We needed to determine whether the lack of ABT-737 efficacy as a single agent was due to the expression of additional BCL2 family members, targetable by the pan-inhibitor obatoclax, or the fact that ABT-737 has recently been demonstrated to be an ABCB1 substrate in chronic lymphocytic leukaemia [47]. The gene discussed is BCL2; the disease is B-cell chronic lymphocytic leukemia.