A Study to Investigate the Safety and Efficacy of Belantamab for the Treatment of Multiple Myeloma When Used as Monotherapy and in Combination Treatments (DREAMM-20)

Inclusion Criteria: Participants at the time of signing the Informed Consent Form (ICF) are at least 18 years old or are of the legal age of consent in the jurisdiction in which the study is taking place. Participants who have histologically or cytologically confirmed diagnosis of Multiple Myeloma (MM), as defined by the IMWG, and measurable disease. PART 1: Participants who have received at least 3 prior lines of anti-myeloma treatments, and have already received an immunomodulating agent, a proteasome inhibitor, and an anti-CD38 mAb (unless contraindicated or unavailable). Lines of therapy are defined by consensus panel of the International Myeloma Workshop. PART 2: Participants who meet all of the following: Have undergone Autologous stem cell transplant (ASCT) or are considered transplant ineligible Have been previously treated with at least ONE prior line of MM therapy Have documented disease progression during or after their most recent therapy PART 3: Participants who meet both of the following: NDMM with a requirement for treatment as documented per IMWG criteria Not considered a candidate for high dose chemotherapy with ASCT due to: Age ≥ 65 years OR Age 18-65 years with presence of comorbid condition(s) likely to have a negative impact on tolerability of high-dose chemotherapy with ASCT or who refuse high-dose chemotherapy with ASCT as an initial treatment. Participants capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and protocol. Exclusion Criteria: Diagnosis of primary Amyloid Light chain (AL) Amyloidosis, active Polyneuropathy, organomegaly, endocrinopathy, myeloma protein, and skin changes (POEMS) syndrome, primary plasma cell leukemia. Any serious and/or unstable pre-existing medical, psychiatric disorder, or other conditions (including lab abnormalities) that could interfere with participant's safety, obtaining informed consent, or compliance with study procedures. Active infection requiring antibiotic, antiviral, or antifungal treatment. Known, current drug or alcohol abuse. Is or has an immediate family member (e.g., spouse, parent/legal guardian, sibling, or child) who is investigational site or Sponsor staff directly involved with this trial, unless prospective Independent Review Board (IRB) approval (by chair or designee) is allowing exception to this criterion for a specific participant.