Study to Assess Change in Disease Activity and Adverse Events of Oral Venetoclax With Intravenous (IV) Obinutuzumab in Adult Participants With Recurring Chronic Lymphocytic Leukemia (CLL)

Chronic lymphocytic leukemia (CLL) is the most common leukemia (cancer of blood cells). The purpose of this study is to assess retreatment with venetoclax-obinutuzumab (VenG) in participants previously treated with fixed duration first-line (IL) therapy of venetoclax in combination with an anti-CD20 antibody +/- X (where X is any additional drug). Adverse events and change in disease activity will be assessed. Venetoclax is an approved drug for the treatment of CLL. Study doctors put the participants in 1 of 2 groups, called cohorts, based on when symptoms of CLL came back after previous treatment in first-line. Approximately 75 adult participants with CLL who have been treated with venetoclax in combination with an anti-CD20 antibody +/- X will be enrolled in the study in approximately 60 sites worldwide. Participants will receive intravenous (IV) obinutuzumab + oral venetoclax (VenG) in 28-day cycles for a total of 6 cycles per cohort, followed by 6 to 18 cycles of venetoclax alone, for a total treatment of 12 to 24 cycles, depending on the cohort. There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.

Inclusion Criteria: * Documented diagnosis of chronic lymphocytic leukemia (CLL) that requires treatment for CLL according to International Workshop for Chronic Lymphocytic Leukemia (iwCLL) 2018 criteria. * Previously completed venetoclax + anti-CD20 antibody +/- X regimen as a fixed duration first-line (1L) therapy and achieved documented response, defined as complete remission, complete remission with incomplete marrow recovery, partial remission, or nodular partial remission. * More than 24 months (Cohort 1) or 12-24 months (Cohort 2) have elapsed between last dose of venetoclax and disease progression after completion of 1L treatment. Exclusion Criteria: \- Received intervening treatment for CLL after completing previous treatment with a venetoclax + anti-CD20 antibody +/- X regimen.