Primary Objective:

1. To describe the distribution of treatment regimens and objective response rate (ORR) in a Benchmark Cohort of real-world patients with relapsed/refractory multiple myeloma (RRMM) who initiate treatment after meeting the following criteria: (1) have either (a) at least three prior lines (3L) and are triple-class exposed (TCE), or (b) are triple-class refractory (TCR), and (2) meet similar inclusion/exclusion criteria to patients in phase 2 cohort 2 of the R5458-ONC-1826 (NCT03761108) trial.

Secondary Objectives:

1. To describe additional outcomes (duration of response [DOR], progression-free survival [PFS], overall survival [OS], and time to next treatment [TTNT]) in the same Benchmark Cohort population described in the primary objective.
2. To describe distribution of treatment regimens, ORR, DOR, PFS, OS, and to compare ORR, PFS, OS, and TTNT in an Analysis Cohort consisting of real-world patients derived from the Benchmark Cohort described above who are weighted to align with the characteristics of patients in phase 2 cohort 2 of the R5458-ONC-1826 (NCT03761108) trial. Comparative analyses of PFS and OS will be performed conditional on sufficient maturity of survival data in the R5458-ONC-1826 (NCT03761108) trial at the time of analysis.

Inclusion Criteria:

1. Eastern Cooperative Oncology Group (ECOG) performance status ≤1 at baseline
2. Confirmed diagnosis of active MM by IMWG diagnostic criteria
3. Have myeloma that is response-evaluable with measurable disease by M-protein in serum or urine as specified in the IMWG response criteria.
4. Triple-class exposed or refractory

Exclusion Criteria:

1. Diagnosis of plasma cell leukemia, primary systemic light-chain amyloidosis (excluding myeloma-associated amyloidosis), Waldenström macroglobulinemia, or polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin (POEMS) changes syndrome
2. Known MM brain lesions or meningeal involvement
3. History of neurodegenerative condition, central nervous system (CNS) movement disorder, or seizure
4. Cardiac ejection fraction <40% by echocardiogram or multi-gated acquisition scan (MUGA) (or a diagnosis of congestive heart failure, cardiomyopathy, or valvular heart disease as a potential proxy)
5. Continuous systemic corticosteroid treatment with more than 10 mg per day of prednisone or anti-inflammatory equivalent
6. Live or live attenuated vaccines
7. Treated with B-cell maturation antigen (BCMA)-directed immunotherapies (BCMA antibody-drug conjugates are not excluded).

Note: Other protocol-defined Inclusion/Exclusion criteria apply

Patients with RRMM who have either at least three prior lines of therapy (LOT) and are triple-class exposed (3L+/TCE), or are triple-class refractory (TCR).