The main purpose of the study is to understand the safety and tolerability of cemsidomide when given along with elranatamab in subjects with relapsed or refractory multiple myeloma.

The first part of the study will evaluate different dose levels of cemsidomide in combination with elranatamab in a limited number of subjects. Approximately 3 different dose levels of cemsidomide in combination with elranatamab may be explored. Once a dose level is determined safe, additional subjects may be enrolled through expansion of the dose level. This expansion will provide further exploration of the safety and evaluation of preliminary antimyeloma activity.

Cemsidomide will be taken orally each cycle for 14 days on/14 days off (1 cycle=28 days). Elranatamab will be administered by subcutaneous injection twice a month. Dexamethasone will be administered weekly until a confirmed response but no longer than 4 cycles.

Inclusion Criteria:

• Diagnosis of multiple myeloma as defined by IMWG criteria
• Measurable disease based on IMWG criteria
• Received 2-4 prior lines of therapy (escalation part) and 1-3 prior lines of therapy (expansion part) for multiple myeloma, consisting of at least 1 immunomodulatory drug (i.e., IKZF 1/3 degrader)
• ECOG performance status 0-2

Exclusion Criteria:

• Active plasma cell leukemia, Smoldering multiple myeloma, POEMS Syndrome, systemic light chain amyloidosis, MDS
• Stem cell transplant within 12 weeks prior to enrollment or active graft vs host disease
• Participants with any active, uncontrolled bacterial, fungal, or viral infection
• Prior treatment with a BCMA-directed TCE or BCMA-directed CAR-T therapy
• Administration with an investigational product within 30 days preceding the first dose of study intervention
• Inability or difficulty swallowing tablets, malabsorption syndrome, or any disease or medical condition significantly affecting gastrointestinal function