Study to Assess Effect of Oral Venetoclax Tablet in Combination With Oral Ibrutinib Capsule on Best Overall Response of Complete Response in Adult Japanese Participants With Relapsed/Refractory Mantle Cell Lymphoma

Mantle Cell Lymphoma (MCL) is a form of Non-Hodgkin Lymphoma (NHL - cancer of the lymphatic system in blood) where cells from outer edge of the lymph nodes, called mantle zone become cancerous. In Japan, MCL accounts for about 3% of all NHL cases. Symptoms of MCL may include enlarged lymph nodes, stomach pain, fever, night sweats, and weight loss. Currently, MCL is not curable with standard therapies. The purpose of this study is to evaluate the safety, efficacy, and effect of venetoclax in combination with ibrutinib on best overall response of complete response in participants with relapsed (return of disease) or refractory (not responding to treatment) (R/R) MCL. Venetoclax is an investigational drug being developed for the treatment of MCL. Ibrutinib is a drug approved for the treatment of MCL. Participants will receive venetoclax (increasing doses) and ibrutinib (fixed dose) for approximately 104 weeks, followed by ibrutinib alone. Adult participants with R/R MCL will be enrolled. Around 12 participants will be enrolled in Japan. Participants will receive oral venetoclax tablet and oral ibrutinib capsule for 104 weeks. After 104 weeks, participants will receive ibrutinib once daily until their disease progresses, or they cannot tolerate the medication, or until they do not want to participate in the study. There may be a higher treatment burden for participants in this study 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, bone marrow biopsies, checking for side effects, and completing questionnaires.