A Safety Study of SGN-CD48A in Patients With Multiple Myeloma

Inclusion Criteria: * Diagnosis of MM requiring systemic therapy (per the International Myeloma Working Group \[IMWG\]) * Patients must not have other therapeutic options known to provide clinical benefit in MM available to them. Prior lines of therapy must include at least a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 antibody. * Measureable disease, as defined by at least one of the following: serum M protein 0.5 g/dL or higher, urine M protein 200 mg/24 hour or higher, and serum immunoglobulin free light chain 10 mg/dL or higher and abnormal serum immunoglobulin kappa lambda free light chain ratio * Adequate hematologic, renal, and hepatic function * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Life expectancy greater than 3 months * A negative pregnancy test (for females of childbearing potential) * Patients must provide written consent Exclusion Criteria: * Pre-existing peripheral neuropathy Grade 2 or higher * History of malignancy other than MM within the past 3 years * Active cerebral/meningeal disease related to the underlying malignancy * Uncontrolled Grade 3 or higher infection * Known to be positive for HIV or hepatitis B, or known to have active hepatitis C infection * Previous allogeneic stem cell transplant * History of cerebral vascular event, unstable angina, myocardial infarction, or cardiac symptoms consistent with congestive heart failure within the last 6 months * Treatment with any known P-gp inducers/inhibitors or strong CYP3A inhibitors within 14 days prior to the first dose of study drug * Prior antitumor therapy that is not completed at least 4 weeks prior to first dose of study drug, or at least 2 weeks if progressing. Prior CAR T-cell therapy must be completed 8 weeks before first dose of study drug. * Females who are pregnant or breastfeeding