Study to Assess Change in Disease Activity and Adverse Events of Oral Venetoclax in Combination With Intravenous (IV) Obinutuzumab or Oral Ibrutinib in Adult Participants With Untreated Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Lymphoma (SLL)

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries, representing approximately 30% of all adult leukemias. There is a large difference in proportion of malignant lymphoma between the United States (US) and Japan was seen in CLL/small lymphocytic lymphoma (SLL) (Japan, 3.2%; US, 24.1%). The purpose of this study is to assess how well venetoclax works in combination with obinutuzumab (V+G, Cohort 1) or with ibrutinib (V+I, Cohort 2) in Japanese participants with previously untreated CLL/Small Lymphocytic Lymphoma (SLL). Adverse events and change in disease activity will be assessed. Venetoclax is an approved drug for the treatment of CLL and SLL. Study doctors put the participants in 1 of 2 groups, called treatment arms, based on variable alternating assignment. Approximately 20 adult participants with previously untreated CLL/SLL will be enrolled in the study in approximately 20 sites in Japan. Participants in group 1 will receive oral venetoclax + intravenous (IV) obinutuzumab (V+G) in 28-day cycles for a total of 12 cycles, and participants in group 2 will receive oral venetoclax + oral ibrutinib (V+I) in 28-day cycles for a total of 15 cycles. 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, and checking for side effects.