Identification of PCWG3 Target Populations Is More Accurate and Reproducible with PSMA PET Than with Conventional Imaging: A Multicenter Retrospective Study.

Prostate-specific membrane antigen (PSMA)-ligand PET is potentially useful for screening of castration-resistant prostate cancer (CRPC) clinical trial target populations. We investigated the impact of PSMA PET on Prostate Cancer Clinical Trials Working Group 3 (PCWG3) clinical subtype classification when compared with conventional imaging (CI). A multicenter retrospective study enrolled patients who had undergone PSMA PET for CRPC, had prostate-specific antigen values of at least 1 ng/mL, and had undergone CI-that is, CT plus bone scanning or whole-body MRI. The clinical PCWG3 subtype was determined for PET versus CI by 3 masked readers. Sixty-seven patients were included, and PSMA PET led to up-staging in 15% (10/67) of patients; of these, 6 of 10 (60%) had nonmetastatic CRPC on CI. PSMA PET resulted in down-staging in 15% (10/67) of patients. Agreement for PET versus CI PCWG3 clinical subtypes was 0.81 versus 0.51, 0.74 versus 0.47, 0.95 versus 0.72, or 0.59 versus 0.66 for local, nodal, bone, or visceral disease, respectively. Despite 70% concordance with CI, PSMA PET demonstrated superior reproducibility and accuracy especially for non-metastatic CRPC and should be implemented in future clinical trial entry procedures.