Inclusion Criteria:

Measurable MM based on modified IMWG guidelines. Defined by at least one of the following:

1. Serum M-protein ≥ 0.5 g/dL by serum electrophoresis (SPEP) or for IgA myeloma, by quantitative IgA
2. Urinary M-protein excretion ≥ 200 mg/24 hours
3. Free Light Chain (FLC) ≥ 100 mg/L, provided that the FLC ratio is abnormal
4. If serum protein electrophoresis is felt to be unreliable for routine M-protein measurement, then quantitative Ig levels by nephelometry or turbidimetry are acceptable
   • Must have previously received ≥ 3 anti-MM regimens including: an alkylating agent, lenalidomide, pomalidomide, bortezomib, carfilzomib, daratumumab, and a glucocorticoid. There is no upper limit on the number of prior therapies provided that all other inclusion/exclusion criteria are met.
   • MM refractory to previous treatment with one or more glucocorticoids, parenteral PI (i.e., bortezomib and/or carfilzomib), IMiD (i.e., lenalidomide and/or pomalidomide), and the anti-CD38 mAb, daratumumab. Refractory is defined as ≤ 25% response to therapy, or progression during therapy or progression within 60 days after completion of therapy.

Exclusion Criteria:

• Active smoldering MM.
• Active plasma cell leukemia.
• Documented systemic amyloid light chain amyloidosis.
• Active CNS MM.