Early Clonal Dynamics During Venetoclax Treatment for Relapsed or Refractory Chronic Lymphocytic Leukemia (CLL)

Background: The drug venetoclax treats chronic lymphocytic leukemia (CLL). Researchers want to find better treatments for CLL. To do that, they need to learn how the drug affects CLL cancer cells and the immune system. Objective: To learn about genetic changes that happen during treatment of CLL with venetoclax. Eligibility: Adults ages 18 and older with relapsed or refractory CLL after at least 1 prior therapy Design: Participants will be screened under a separate protocol. In Phase 1, participants will get venetoclax free of charge through the NIH. Venetoclax is started at a low dose. The dose will be increased every week until participants reach their maximum tolerable dose. This usually take about 5 weeks. Participants will visit the NIH at least once per week. Visits will be about 4 hours. They may have to stay in the hospital to be observed. In Phase 2, participants will continue to get the drug through their local cancer doctor and their health insurance. Patients will also visit the NIH every 6 months, or if their disease progresses. At the NIH participants will have regular health assessments. These will include physical exams and a review of the medicines they are taking. They will talk about how they are feeling. The study included the following tests: Blood draws CT scans: Participants will lie in a machine that takes pictures of the body (maximum 3 per year) Bone marrow biopsies: A small amount of marrow will be taken out of the participant s hip bone with a needle. Optional lymph node biopsies: A small piece of the participant s tissue will be taken out with a needle. The study will last at least 2 years.