However, in refractory CLL, initial results of ABT-199 treatment have shown potential for tumor lysis syndrome, requiring slow dose escalation.17, 18, 23 Binding affinity studies with fluorescence polarization assay and TR-FRET showed that ABT-199 has very weak affinity for BCL-xL and MCL-1. The gene discussed is BCL2L1; the disease is B-cell chronic lymphocytic leukemia.