Effect of total antibody mass on tracer distribution. Total of 74 MBq (2 mCi) of immuno-PET antibody composed of native daratumumab labeled with positron-emitting radionuclide zirconium 89 (89Zr) through chelator deferoxamine (DFO), or 89Zr-DFO-daratumumab, was administered to study participants with CD38-positive multiple myeloma at total antibody masses of, A, 3-mg total antibody mass (3-mg radiolabeled and 0-mg cold antibody) in study participant 7, a 60-year-old man; B, 20-mg total antibody mass (3-mg radiolabeled and 17-mg cold antibody) in study participant 9, an 80-year-old man; and, C, 50-mg total antibody mass (3-mg radiolabeled and 47-mg cold antibody) in study participant 3, a 62-year-old man. All maximum intensity projection images were obtained 5–6 days following tracer administration. Higher physiologic splenic uptake at 3-mg total antibody mass is relatively reduced at 20-mg and 50-mg total antibody doses. Foci consistent with 89Zr-DFO-daratumumab–avid osseous myeloma are visualized at 20-mg and 50-mg total antibody doses.