Official title: A Phase 3, Open-label, Randomized Study to Compare the Efficacy and Safety of Nemtabrutinib (MK-1026) Plus Venetoclax Versus Venetoclax Plus Rituximab in Participants With Relapsed/Refractory Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma Following at Least 1 Prior Therapy (BELLWAVE-010) Summary: The purpose of this study is to assess the safety and tolerability and to confirm the dose of nemtabrutinib in combination with venetoclax in participants with R/R CLL/SLL. The primary study hypotheses are that the combination of nemtabrutinib plus venetoclax is superior to VR with respect to progression-free survival (PFS) per 2018 International Workshop on Chronic Lymphocytic Leukemia (iwCLL) criteria as assessed by blinded independent central review (BICR). Conditions: Leukemia, Lymphocytic, Chronic, B-Cell, Leukemia, Chronic Lymphocytic, Small-Cell Lymphoma, Lymphoma, Small Lymphocytic, CLL, SLL Study type: INTERVENTIONAL Primary purpose: TREATMENT Phases: PHASE3 Enrollment: 735 (ESTIMATED) Status: RECRUITING Completion: 2035-07-01 (ESTIMATED)