In the study, 42 patients with relapsed and/or refractory multiple myeloma who had progression after at least two prior lines of treatment (including a proteasome inhibitor and an immunomodulatory imide drug) received AMG 420 at varying doses [0.2 to 800 µg/day (d)]. AMG 420 induced clinical responses in 13 patients, including complete responses (CR) in seven patients. Four patients treated at the 400 µg/d dose achieved minimal residual disease (MRD) negative complete responses, meaning that no cancer cells were detectable in the bone marrow. The objective response rate at 400 µg/d was 70 percent (seven of 10 patients), with six patients still responding up to 7.5 months. One dose-limiting toxicity was observed up to the 400 µg/d dose (peripheral polyneuropathy, which improved to baseline after intravenous immunoglobulin and corticosteroid treatment).