Study Evaluating AMG 424 in Subjects With Multiple Myeloma

Inclusion Criteria: * Multiple myeloma meeting the following criteria: * Pathologically-documented diagnosis of multiple myeloma that has relapsed after at least two prior lines of therapy that must include a proteasome inhibitor (PI), immunomodulatory drug (IMiD), and, where approved and available, anti-CD38 therapy in any order OR that is refractory to PI, IMiD, and anti-CD38 therapy. ◾Subjects who could not tolerate a PI, IMiDs, or a CD38-directed therapeutic antibody due to unacceptable toxicities are eligible to enroll in the study. * Measurable disease as per IMWG response criteria * Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 2 Exclusion Criteria: * Known central nervous system involvement by multiple myeloma * Previously received allogeneic stem cell transplant and one or more of the following: * received the transplant \< 6 months prior to study Day 1 * received immunosuppressive therapy \< 3 months prior to study Day 1 * any active acute graft versus host disease (GvHD), grade 2- 4, according to the Glucksberg criteria or active chronic GvHD requiring systemic treatment * any systemic therapy against GvHD \< 2 weeks prior to study Day 1 * Autologous stem cell transplantation less than 90 days prior to study day 1 * Multiple myeloma with IgM subtype * POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes) * Evidence of primary or secondary plasma cell leukemia at the time of screening * Waldenstrom's macroglobulinemia * Amyloidosis * Dexamethasone at cumulative doses of greater than 160 mg or equivalent \<3 weeks prior to study Day 1 is not allowed. Use of topical or inhaled steroids is acceptable * Anticancer treatment (chemotherapy, IMiD, PI, molecular targeted therapy) \< 2 weeks prior to study Day 1 * Treatment with a therapeutic antibody targeting CD38 \< 12 weeks prior to study Day 1 * Systemic radiation therapy or major surgery \< 28 days prior to study Day 1 as well as focal radiotherapy \< 14 days prior to study Day 1. * Major surgery within 28 days prior to study Day 1