The purpose of this study is to investigate the efficacy and safety of BGB-16673 compared with investigator's choice (idelalisib plus rituximab \[for CLL only\] or bendamustine plus rituximab or venetoclax plus rituximab retreatment) in participants with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL) previously exposed to both BTK inhibitors (BTKi) and BCL2 inhibitors (BCL2i).
Confirmed diagnosis of CLL or SLL, requiring treatment, based on 2018 international workshop on chronic lymphocytic leukemia (iwCLL) criteria.
Previously received treatment for CLL/SLL with both a BTKi and a BCL2i.
Participants with SLL must have measurable disease by computer tomography (CT)/magnetic resonance imaging (MRI)
Eastern Cooperative Oncology Group (ECOG) score 0, 1, or 2
Known prolymphocytic leukemia or history of, or currently suspected, Richter's transformation
Prior autologous stem cell transplant or chimeric antigen receptor-T cell therapy in the last 3 months
Known central nervous system involvement
Prior exposure to any BTK protein degraders