 - The participant has active central nervous system CNS or leptomeningeal metastasis brain metastasis at the time of enrollment Phase 1b or randomization Phase 2. Participants with a history of a CNS metastasis previously treated with curative intent for example, stereotactic radiation or surgery that have not progressed on follow-up imaging, have been asymptomatic for at least 60 days, and are not receiving systemic corticosteroids and oranticonvulsants, are eligible. Participants with signs or symptoms of neurological compromise should have appropriate radiographic imaging performed before enrollment Phase 1b randomization Phase 2 to rule out brain metastasis. 