A Study Designed to Evaluate the Safety and Efficacy of Venetoclax Plus Dexamethasone (VenDex) Compared With Pomalidomide Plus Dexamethasone (PomDex) in Participants With t(11;14)-Positive Relapsed or Refractory Multiple Myeloma.

Inclusion Criteria:

Documented diagnosis of multiple myeloma (MM) based on standard International Myeloma Working Group (IMWG) criteria.
Measurable disease at screening as defined per protocol.
Has received at least 2 prior lines of therapy as described in the protocol.
Has had documented disease progression on or within 60 days after completion of the last therapy.
Has received at least 2 consecutive cycles of lenalidomide and be relapsed/refractory to lenalidomide, as defined per protocol.
Has received at least 2 consecutive cycles of a proteasome inhibitor (PI).
Has t(11;14)-positive status determined by an analytically validated fluorescent in situ hybridization (FISH) assay per centralized laboratory testing.
An Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to 2.
Laboratory values (liver, kidney and hematology laboratory values) that meet criteria as described per protocol.

Exclusion Criteria:

History of treatment with venetoclax or another B-Cell Lymphoma (BCL)-2 inhibitor or pomalidomide.
History of other active malignancies, including myelodysplastic syndromes (MDS), within the past 3 years (exceptions described in the protocol).
Evidence of ongoing graft-versus-host disease (GvHD) if prior stem cell transplant (SCT).
Prior treatment with any of the following: allogeneic or syngeneic SCT within 16 weeks prior to randomization; or autologous SCT within 12 weeks prior to randomization.
Known central nervous system involvement of MM.
Concurrent conditions as listed in the protocol.