Relapsed or Refractory Multiple Myeloma: ABBV-383 vs Standard Available Therapies in Subjects with RRMM (3L+ RRMM Monotherapy Study)

Multiple myeloma (MM) is a cancer of the blood's plasma cells. The cancer is typically
found in the bones and bone marrow (the spongy tissue inside of the bones) and can cause
bone pain, fractures, infections, weaker bones, and kidney failure. Treatments are
available, but MM can come back (relapsed) or may not get better (refractory) with
treatment. This is a study to determine change in disease symptoms of etentamig compared
to standard available therapies in adult participants with relapsed/refractory (R/R) MM.

Etentamig is an investigational drug being developed for the treatment of R/R MM. This
study is broken into 2 Arms; Arm A and Arm B. In Arm A, participants will receive
etentamig as a monotherapy. In Arm B, participants will receive the standard available
therapy (SAT) identified by the Investigator during screening, in accordance with the
local (or applicable) approved label, package insert, summary of product characteristics,
and/or the institutional guidelines, as applicable. Around 380 adult participants with
relapsed/refractory multiple myeloma will be enrolled at approximately 140 sites across
the world.

In Arm A participants will receive etentamig as an infusion into the vein in 28 day
cycles, during the 3.5 year study duration. In Arm B, participants will receive the SAT
identified by the Investigator during screening, in accordance with the local (or
applicable) approved label, package insert, summary of product characteristics, and/or
the institutional guidelines, as applicable, during the 3.5 year study duration.

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, checking for side effects and questionnaires.

Inclusion Criteria:

- Eastern Cooperative Oncology Group (ECOG) performance of <= 2.

- Diagnosis of relapsed/refractory (R/R) multiple myeloma (MM) during or after the
participant's last treatment as stated in the protocol.

- Must have measurable disease with at least 1 of the following assessed within 28
days of enrollment:

- Serum M-protein >= 0.5 g/dL (>= 5 g/L).

- Urine M-protein >= 200 mg/24 hours.

- In participants without measurable serum or urine M protein, serum free light
chain (FLC) >= 100 mg/L (10 mg/dL) (involved light chain)and an abnormal serum
kappa lambda ratio.

- Must have received at least 2 or more lines of therapy, including a proteasome
inhibitor (PI), an immunomodulatory imide (IMiD), and an anti-CD38 monoclonal
antibody (mAb).

- Must be eligible to receive the Investigator's choice standard available therapy
(SAT) based on approved prescribing information, previous MM treatment history, and
institutional guidelines.

Exclusion Criteria:

- Clinically significant (per Investigator's judgment) drug or alcohol abuse within
the last 6 months.

- Clinically significant conditions such as but not limited to the following:
neurologic, psychiatric, endocrine, metabolic, immunologic, cardiovascular,
pulmonary, or hepatic disease within the last 6 months that would adversely affect
the participant's participation in the study.

- Central nervous system involvement of MM.

- Has received B-cell maturation antigen (BCMA)-targeted therapy.