Objective: Miltuximabâ is a chimeric antibody targeting Glypican-1 which is overexpressed in prostate cancer. This Phase I trial uses a single dose (250 MBq, 1 mg) of Miltuximabâ conjugated with the chelator (DOTA) radiolabelled with 67 Ga (Gallium-67) with aims to establish dose safety and tolerability. Methods: Metastatic patients are dosed with unlabelled Miltuximabâ conjugated with DOTA followed by the infusion of 67 Ga-Miltuximabâ an hour after. Patients undergo whole body c-camera scans and SPECT/CT scans up to 144 hours postinfusion. Standard of care imaging is performed at least 14 days before and after participation. Between cohorts, safety is evaluated by an external monitoring committee. Results: Ten of twelve patients have been enrolled into the trial. Miltuximabâ is well tolerated and does not elicit any drug-related adverse reactions. 30 minutes post-67Ga-Miltuximabâ dose, intense mediastinal uptake was observed, followed by liver and spleen uptake from 30 min to 72 h post dose. Conclusions: This study is the ﬁrst in human for Miltuximabâ and demonstrates its potential for further clinical evaluation as a theranostic in prostate cancers.