Nemtabrutinib for Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Leukemia (SLL) Refractory to Covalent Bruton Tyrosine Kinase Inhibitor or Pirtobrutinib and Previously Treated With a BCL2 Inhibitor

Background: Chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL) are diseases in which the body makes too many white blood cells that do not work properly. Because white cells play a role in immune function, people with CLL/SLL may be at greater risk of infections. CLL/SLL can be controlled with drugs, but many people develop resistance, and the treatments stop working. Objective: To test a new drug (nemtabrutinib) in people with CLL/SLL. Eligibility: People aged 18 years or older with CLL/SLL that persists despite treatment. Design: Participants will be screened. They will have imaging scans, blood and urine tests, and a test of their heart function. They will have a bone marrow biopsy: a sample of tissue and fluids will be drawn from inside their hip bone. They may also have a sample cut from a swollen lymph node, if one is safe to access. Nemtabrutinib is a tablet taken by mouth. Participants will take the drug once a day at home in 4-week cycles. They will have clinic visits at least every 4 weeks for the first 6 months and then every 3 months after that. Biopsies, imaging exams, and other tests may be repeated at these visits. Participants may also undergo lymphapheresis: Blood will be drawn from a tube inserted into a vein. The blood will pass through a machine that separates out cancer and immune cells. The remaining blood will be returned to the body through a different tube. Participants may stay in the study as long as the drug is helping them.