Testing the Addition of KRT-232 (AMG 232) to Usual Chemotherapy for Relapsed Multiple Myeloma

Inclusion Criteria: * Subjects must have histologically confirmed diagnosis of multiple myeloma * Subjects must have measurable disease, as defined by at least one of the following: * Serum monoclonal protein M-protein level \>= 0.5 g/dL * Urinary M-protein excretion of \>= 200 mg over a 24-hour period * Involved free light chain level \>= 10 mg/dL, along with an abnormal free light chain ratio * Subjects must have disease that has relapsed and/or refractory after their most recent therapy, with progressive disease (PD) being defined as an increase of 25% from the lowest response value in any one or more of the following: * Serum M-component protein (the absolute increase must be \>= 0.5 g/dL) and/or * Urine M-component protein (the absolute increase must be \>= 200 mg/24 hours) and/or * Only in subjects without a measurable serum and urine M protein level: the difference between involved and uninvolved free light chain (FLC) levels (absolute increase) must be \> 10 mg/dL * Definite development of new bone lesions or soft tissue plasmacytomas or definite increase in the size of existing bone lesions or soft tissue plasmacytomas * Development of hypercalcemia (corrected serum calcium \> 11.5 mg/dL) that can be attributed solely to the plasma cell proliferative disorder * Subjects with one to three lines of therapy for their disease with a line of therapy defined as one or more cycles of a planned treatment program; using this definition, treatment with induc…