PI left institution and study is being transferred.

The purpose of this study is to see if using the radioactive tracer 89Zr-DFO-daratumumab with PET/CT scans is a practical and effective way to view and monitor multiple myeloma in participants before and during their treatment with daratumumab. We also want to see if 89Zr-DFO-daratumumab PET/CT scans can predict a participant's response to therapy, and if they can better locate any leftover disease following treatment compared to the standard imaging methods.

Inclusion Criteria:

• Age ≥ 21 years
• Histologically/immunohistochemistry-confirmed CD38-positive multiple myeloma
• At least one tumor lesion on CT, MRI, or FDG PET/CT within 90 days of protocol enrollment
• ECOG performance status 0 to 2
• Participant is capable of having an informed consent discussion (Legally Authorized Representatives are not permitted to sign on a participant's behalf).

Exclusion Criteria:

• Life expectancy < 12 months
• Pregnancy or lactation
• Patients who cannot undergo PET/CT scanning because of weight limits. PET/CT scanners may not be able to function with patients over 450 pounds.
• History of anaphylactic reaction to humanized or human antibodies.
• Previous treatment with daratumumab. Previous treatment with other myeloma therapies will be allowed.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.