A Randomized Phase II Study Of Bruton Tyrosine Kinase Inhibitor With Or Without Venetoclax In Veterans With Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Lymphoma (SLL)

People who have chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) are often treated with ibrutinib, acalabrutinib, or zanubrutinib. These are pills that are taken by mouth. This type of pill is called a "Bruton Tyrosine Kinase Inhibitor" or BTKi. Another treatment for CLL/SLL is a different pill called venetoclax. People with CLL/SLL who are currently taking BTKi as their treatment must continue to take the medicine for the rest of their lives (unless it is no longer working or causing difficult side effects). New studies tested the combination of BTKi and venetoclax for one to two years, and showed that it was a very effective treatment, and allowed patients to stop therapy. The investigators don't know if adding venetoclax in patients who have already taken BTKi therapy for at least six months and who are responding to it will help control the CLL/SLL better and if it will allow them to stop treatment safely. Also, the investigators don't know how the side effects and effectiveness of the combination will be in Veterans. The investigators also don't know how a patient's quality of life will be affected if they continue BTKi by itself or if they take the combination and then are able to stop treatment. If participants meet the eligibility criteria, they will be randomly assigned a study treatment. This study has 2 main study groups: ARM A (BTKI ALONE): There will be about 50 people in this group. ARM B (BTKI PLUS VENETOCLAX): There will be about 50 people in this group. The participants will not be charged for any treatments or procedures that are part of this study. If participants usually pay co-payments for VA care and medications, they will still pay these co-payments for VA care and medications that are not part of this study.