Inclusion Criteria
Subjects eligible for inclusion in this study must meet all the following criteria:
1. Be willing and able to provide signed informed consent for the study.
2. Age ≥18 years at the time of signed consent.
3. ECOG Performance Status ≤2.
4. Subjects must have a documented diagnosis of MM and measurable disease at
enrollment. Measurable disease is defined as follows:
• Serum M-protein by sPEP ≥0.5 g/dL
• Serum dFLC >10 mg/dL with an abnormal kappa/lambda (κ/λ) ratio (1.65)
• Urine M-protein by uPEP ≥200 mg/24-hour urine
5. For prior treatments, subjects must have the following:
• Received at least 3 prior antimyeloma regimens (for a minimum of 2 or more
consecutive cycles) that must have included an immunomodulatory drug (i.e.,
IKZF1/3 degrader), a proteasome inhibitor, an anti-CD38 antibody, and a TCE or
CAR-T therapy, unless not indicated and/or patient refusal.
• Refractory to or had documented disease progression within 60 days from the last
dose of their prior MM treatment (or, if the last MM therapy was with CAR-T cells,
documented disease progression any time after administration).
6. Subjects must be able to provide a BMA and/or BMB during screening or use an archival
sample (within 6 months of screening visit) for chromosomal abnormalities (FISH)
(Section 8.2.2).
7. Subjects need to have adequate organ function defined as follows:
• ANC ≥1.0 × 109/L assessed at least 5 days after receiving G-CSF, and after at least
10 days after receiving pegfilgrastim.
• Platelets ≥75,000 cells/μL at least 5 days after receiving a platelet transfusion or use
of platelet-stimulating drugs (e.g., romiplostim or eltrombopag).
• Hemoglobin ≥8.0 g/dL independent of transfusion support for at least 7 days after
blood transfusion or use of erythropoietin.
• ALT and AST ≤3.0 × ULN; except for subjects who have tumor infiltration of the
liver, where ALT or AST ≤5 × ULN.
• Total bilirubin ≤1.5 × ULN (unless due to Gilbert’s syndrome; total bilirubin should
be ≤3.0 × ULN).
• CrCl ≥40 mL/min (Cockcroft-Gault equation, or per institutional standard, or directly
measured).
• Corrected serum calcium ≤13.5 mg/dL (≤3.5 mmol/L).
• INR must be on a stable regimen and have INR and aPTT within the therapeutic range for
the anticoagulant regimen).
8. Toxicities from prior anticancer therapies must have resolved to baseline severity or
CTCAE Grade ≤1.
9. Female subjects may not be pregnant or intend to become pregnant, may not breastfeed
or intend to breastfeed, or donate ova during their participation in this study until 30 days
after the last dose of study treatment, must agree to the pregnancy testing and highly
effective contraception requirements of the study (Section 11.2).
• Subjects of childbearing potential must agree to use highly effective contraception, as
defined in Section 11.2, during their participation in the study until 30 days after the
completion of study treatment.
• Subjects on HRT and whose menopausal status is in doubt will be required to use one
of the contraception methods (per Section 11.2) specified if they wish to continue
their HRT during the study.
• Subjects of nonchildbearing potential (i.e., physiologically incapable of becoming
pregnant), defined as (a) premenopausal female with documented history of bilateral
salpingo-oophorectomy or hysterectomy; (b) postmenopausal female, defined as
12 months of spontaneous amenorrhea without an alternative medical cause which
can be confirmed in questionable cases, by a serum FSH >40 MIU/ML.
10. Male subjects must agree to use a condom when having intercourse with a person of
childbearing potential during the Treatment Period and for at least 30 days after the last
dose of study treatment.
11. Male subjects must refrain from donating sperm during the Treatment Period and for
30 days after discontinuation.
12. Subjects must refrain from donating blood during study treatment and for 30 days after
discontinuation.

Exclusion Criteria
Subjects eligible for this study must not meet any of the following criteria:
1. Presence of myeloma in the CNS.
2. Has received prior plasmapheresis and/or radiotherapy within 2 weeks of start of study
treatment.
3. Subjects with any of the following:
• Nonsecretory or oligosecretory MM
• Systemic light chain amyloidosis
• Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal gammopathy, and Skin
changes (POEMS) Syndrome
• MDS
4. Treatment with mezigdomide or iberdomide during the subject’s most recent line of
therapy.
5. Previously treated with cemsidomide.
6. Peripheral neuropathy ≥Grade 2 at screening.
7. Clinically significant impaired cardiac function or cardiac disease, including the
following:
• LVEF • Clinically significant and/or uncontrolled heart disease such as congestive heart
failure requiring treatment (NYHA ≥Grade 2), uncontrolled hypertension, or
clinically significant arrhythmia.
• Average QTcF >480 msec on screening ECG (for subjects with pacemakers or bundle
branch block that distort the QT interval, consult the sponsor medical monitor).
• Acute myocardial infarction or unstable angina pectoris within 6 months prior to
study entry.
8. Thromboembolic event within 3 months prior to enrollment. Enrolled subjects must have
a risk-based prophylaxis for venous thromboembolism as described in Section 6.2.1.4.
9. Known malignancy other than study indication that has progressed or required treatment
within the past 3 years. A history of localized or noninvasive cancers such as basal or
squamous cell carcinoma of the skin or carcinoma in situ (e.g., breast carcinoma, cervical
cancer in situ) may be acceptable and must be approved by the sponsor.
10. Major surgery within 2 weeks of the first dose of study treatment.
11. Received live, attenuated vaccine within 4 weeks of first dose.
12. Known history of HIV infection.
13. Any subject with a known history of, or considered at risk for, Hepatitis B infection must
be tested. Subjects will be excluded if HBsAg is detected. If a subject has undetectable
HBsAg but has detectable HBc and anti-HBsAg antibodies, they may be enrolled if
serum hepatitis B DNA is undetectable by a PCR-based assay.
14. Any subject with a known history or risk of HCV must test negative for anti-HCV
antibodies. If anti-HCV antibodies are present or there is a prior history of HCV
treatment, HCV RNA must be undetectable.
15. Any active, uncontrolled bacterial, fungal, or viral infection (including pneumonitis) or
any life-threatening illness, medical condition, or organ system dysfunction which, in the
investigator’s opinion, could compromise the subject’s safety or put the study outcomes
at undue risk.
16. Concurrent administration of strong CYP3A inducers or inhibitors, including certain
foods, and inhibitors of P-gp and BCRP. Strong CYP3A inhibitors and inhibitors of P-gp
and BCRP must be discontinued 5 half-lives before the first dose of study drug, and
strong CYP3A inducers must be discontinued 14 days prior to the first dose of study drug
(Section 6.4.3).
Note: If a subject can be switched to a similar agent that is not a strong CYP3A
modulator or is a weak CYP3A modulator they may be permitted to enroll in the study.
17. Patient has received prior treatment for MM (approved or investigational) ≤5 half-lives or
4 weeks (whichever is shorter) prior to the first dose of study treatment.
18. Inability or difficulty swallowing tablets, malabsorption syndrome, or any disease or
medical condition significantly affecting gastrointestinal function.
19. Has a history or current evidence of any condition, therapy, or laboratory abnormality
that might confound results of the study, interfere with the subject’s participation for full
duration of the study, or is not in the best interest of the subject to participate, in the
opinion of the treating investigator.
20. Has a known psychiatric or substance abuse disorder that would interfere with
cooperating with requirements of the study.
21. Previously identified hypersensitivity to components of the study treatment or excipients.