A Study of Venetoclax in Participants With Relapsed or Refractory Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma

This is a Phase 2, open-label, multicenter study, evaluating the efficacy of venetoclax in participants with relapsed or refractory Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Lymphoma (SLL) either in presence of 17p deletion (Cohort 1) or those who have failed a B-receptor signaling pathway inhibitor (BCRI) therapy and who have also failed, or were unable to receive chemoimmunotherapy (CIT) irrespective of 17p status (Cohort 2).

Inclusion Criteria: * Participant must have a diagnosis of relapsed or refractory chronic lymphocytic leukemia (CLL)/Small Lymphocytic Lymphoma (SLL) that meets 2008 Modified International Workshop for Chronic Lymphocytic Leukemia (iwCLL) National Cancer Institute-Working Group (NCI-WG) Guidelines and the following: * Participant must have an indication for treatment according to the 2008 Modified iwCLL NCI-WG Guidelines. * SLL participant must have measurable disease (B-lymphocytosis greater than 5 × 10\^9/L or an enlarged lymph node(s) (Longest Diameter (LDi) \> 1.5 cm at baseline) or hepatomegaly or splenomegaly due to CLL). * SLL participant must have presence of lymphadenopathy and absence of cytopenias caused by a clonal marrow infiltrate. * Participant must have relapsed or refractory CLL/SLL after receiving at least one prior line of therapy. * Participants (in Cohort 1) must have 17p deletion, assessed by a central laboratory. * Participants (in Cohort 2) must meet both of the following: * Relapsed/refractory disease to B-Cell Receptor Signaling Pathway Inhibitor (BCRI) treatment; * And either of the following: (a) relapsed/refractory disease to chemoimmunotherapy (CIT), or (b) ineligible to receive CIT, defined as having known 17p deletion or TP53 mutation, or Cumulative Illness Rating Scale (CIRS) \>6 or calculated creatinine clearance \