Pathologic correlation of 89Zr-Df-IAB2M antiprostate-specific membrane antigen (PSMA) minibody in patients with metastatic prostate cancer.

220 Background: IAB2M is a novel anti-PSMA minibody (Mb) based on the humanized J591 antibody that targets the extracellular domain of PSMA. The Mb has been engineered to remove Fc-Rn interactions and reduce the molecular weight relative to J591. The result is faster blood pool clearance, for a more favorable imaging schedule, while retaining bivalent targeting of PSMA. We have previously reported on the pharmacokinetics, dosimetry, and lesion uptake of IAB2M(Pandit-Taskar et al, WMIS 2014). Here we report the correlation between imaging and pathology of biopsies of PSMA avid lesions. Methods: Following standard imaging (SI) of CT/MRI, bone scintigraphy (BS), and FDG PET, 5 mCi of 89Zr-Df-IAB2M was administered intravenously. Escalating minibody doses of 10, 20, and 50 mg were delivered, with cohort expansion at 10 and 20 mg. Whole body PET/CT scans were serially performed at various time points:1-2 h, 24 h, 48 h, and 72-144 h post injection. Metastases identified on PET were confirmed, where possible, wi...