Here, we present results from the phase I clinical trial to assess the safety, tolerability, and pharmacokinetics (PK) of lorvotuzumab mertansine when administered as monotherapy to patients with CD56-positive (CD56+) relapsed or RRMM….Despite a high proportion of patients with relapsed and/or refractory MM (56.8%), stable disease or better was noted in 42.9% of patients, and these patients had a long duration of response (median, 15.5 months).