The BCL2 antagonist venetoclax (GDC-0199/ABT-199) showed striking activity with tumor lysis syndrome as dose limiting toxicity in patients with relapsed and refractory CLL. 400 mg venetoclax was determined to be a safe and efficacious dose. Several patients treated with the combination of venetoclax and rituximab in relapsed refractory CLL even achieved MRD negativity. The FDA approved Venetoclax for the treatment of relapsed CLL with 17p/TP53 on 12th April 2016.