Inclusion Criteria: Subjects must satisfy the following criteria to be enrolled in the study: 1. Subject must understand and voluntarily sign an informed consent form (ICF) prior to any study-related assessments/procedures being conducted. 2. Subject (male or female) is ≥ 18 years of age the time of signing the ICF. 3. Subject has non-secretory multiple myeloma, plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes) syndrome, or amyloidosis. 4. Subjects must have measurable disease (as determined by the central lab). 5. Subject consents to hospitalization for monitoring and collection of study peripheral blood samples. 6. Subject consents to serial bone marrow aspirations and/or biopsies during Screening, study treatment and at the end of treatment. 7. Subject has an Eastern Cooperative Oncology Group (ECOG) PS of 0 or 1. 8. Subjects must have adequate hematologic, liver, renal, and coagulation function as assessed by laboratory tests. 9. Females and males must practice true abstinence or agree to contraceptive methods throughout the study, and during the safety follow-up period. Exclusion Criteria: The presence of any of the following will exclude a subject from enrollment: 1. Unless otherwise specified, Subject has received prior investigational therapy directed at B cell maturation antigen (BCMA). In selected cohort(s) of Parts A and B, prior therapy directed at BCMA may be required for enrollment 2. Subject has symptomatic central nervous system involvement of multiple myeloma. 3. Subject has non-secretory multiple myeloma, plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes), or amyloidosis. 4. Subject is on chronic systemic immunosuppressive therapy or corticosteroids. 5. Subjects with clinically significant cardiac disease. 6. Subject had a prior autologous stem cell transplant ≤ 3 month prior to starting CC-93269. 7. Subject had a prior allogeneic stem cell transplant ≤ 12 month prior to starting CC-93269. 8. Subject had a prior systemic cancer-directed treatments or investigational modalities ≤ 5 half-lives or 4 weeks prior to starting CC-93269, whichever is shorter. Subjects must have recovered from any clinically significant non-hematologic toxicities (ie, to Grade ≤1) of prior systemic anti-cancer directed treatments unless otherwise specified 9. Subject had major surgery ≤ 2 weeks prior to starting CC-93269. 10. Subject is a pregnant or lactating female. 11. Subject has known history or serologic evidence of human immunodeficiency virus (HIV) infection. 12. Subject has known history, virologic or serological evidence of hepatitis B or C virus (HBV/HCV) infection. Subjects who had HCV but have received an antiviral treatment and show no detectable HCV viral RNA for 6 months are eligible 13. Subject has a history of a venous thromboembolic event (VTE) within 6 months prior to study entry (eg, deep-vein thrombosis or pulmonary embolism). Subjects with distant history of VTE (ie, occurring > 6 months prior to study entry) who require ongoing treatment with chronic, therapeutic dosing of anti-coagulants (eg, warfarin, low molecular weight heparin, Factor Xa inhibitors) are eligible for study entry. 14. Subject has a history of concurrent second cancers requiring active, ongoing systemic treatment. 15. Subject has a history or presence of clinically relevant central nervous system (CNS) pathology. 16. Subject has any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from participating in the study. 17. Subject has any condition (eg, active or uncontrolled infection) including the presence of laboratory abnormalities, which places the subject at unacceptable risk if he/she were to participate in the study. . 18. Subject has any condition that confounds the ability to interpret data from the study. 19. Subject has inadequate pulmonary function. 20. Subject has active, uncontrolled, or suspected infection.