Venetoclax Treatment (26 Cycles) With 6 Cycles or 12 Cycles of Epcoritamab in Patients With Relapsed or Refractory CLL or SLL

This study is testing a combination of venetoclax (a targeted pill that helps cancer cells self-destruct) and epcoritamab (an immunotherapy injection that directs the immune system to attack cancer) in people with relapsed or refractory chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) — blood cancers that have returned or stopped responding to prior treatments. **You may be eligible if...** - You are 18 or older with CLL or SLL that has come back or stopped responding to treatment - You have received at least one prior systemic treatment - Your CLL/SLL now requires treatment again - Your blood counts, liver, and kidney function are at acceptable levels - If you previously had venetoclax, it must have ended at least 24 months ago and your disease must not have progressed while on it **You may NOT be eligible if...** - You have never been treated for CLL/SLL before - You previously progressed while on venetoclax - You have active infections - You are pregnant or breastfeeding - Your organ function is too impaired to tolerate the treatment Talk to your doctor to see if this trial is right for you.