Reproducibility and Accuracy of the PRIMARY Score on PSMA PET and of PI-RADS on Multiparametric MRI for Prostate Cancer Diagnosis Within a Real-World Database.

The PRIMARY score is a 5-category scale developed to identify clinically significant intraprostate malignancy (csPCa) on 68Ga-prostate-specific membrane antigen (PSMA)-11 PET/CT (68Ga-PSMA PET) using a combination of anatomic site, pattern, and intensity. Developed within the PRIMARY trial, the score requires evaluation in external datasets. This study aimed to assess the reproducibility and diagnostic accuracy of the PRIMARY score in a cohort of patients who underwent multiparametric MRI (mpMRI) and 68Ga-PSMA PET before prostate biopsy for the diagnosis of prostate cancer. Methods: In total, data from 242 men who had undergone 68Ga-PSMA PET and mpMRI before transperineal prostate biopsy were available for this ethics-approved retrospective study. 68Ga-PSMA PET and mpMRI data were centrally collated in a cloud-based deidentified image database. Six experienced prostate-focused nuclear medicine specialists were trained (1 h) in applying the PRIMARY score with 30 sample images. Six radiologists experienced in prostate mpMRI read images as per the Prostate Imaging-Reporting and Data System (PI-RADS), version 2.1. All images were read (with masking of clinical information) at least twice, with discordant findings sent to a masked third (or fourth) reader as necessary. Cohen κ was determined for both imaging scales as 5 categories and then collapsed to binary (negative and positive) categories (score 1 or 2 vs. 3, 4, or 5). Diagnostic performance parameters were calculated, with an International Society of Urological Pathology grade group of at least 2 (csPCa) on biopsy defined as the gold standard. Combined-imaging-positive results were defined as any PI-RADS score of 4 or 5 or as a PI-RADS score of 1-3 with a PRIMARY score of 3-5. Results: In total, 227 patients with histopathology, 68Ga-PSMA PET, and mpMRI imaging before prostate biopsy were included; 33% had no csPCa, and 67% had csPCa. Overall interrater reliability was higher for the PRIMARY scale (κ = 0.70) than for PI-RADS (κ = 0.58) when assessed as a binary category (benign vs. malignant). This was similar for all 5 categories (κ = 0.65 vs. 0.48). Diagnostic performance to detect csPCa was comparable between PSMA PET and mpMRI (sensitivity, 86% vs. 89%; specificity, 76% vs. 74%; positive predictive value, 88% vs. 88%; negative predictive value, 72% vs. 76%). Using combined imaging, sensitivity was 94%, specificity was 68%, positive predictive value was 86%, and negative predictive value was 85%. Conclusion: The PRIMARY score applied by first-user nuclear medicine specialists showed substantial interrater reproducibility, exceeding that of PI-RADS applied by mpMRI-experienced radiologists. Diagnostic performance was similar between the 2 modalities. The PRIMARY score should be considered when interpreting intraprostatic PSMA PET images.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2023 Nov 30 [Epub ahead of print]

Louise Emmett, Nathan Papa, William Counter, Jeremie Calais, Francesco Barbato, Irene Burger, Matthias Eiber, Matthew J Roberts, Shikha Agrawal, Anthony Franklin, Alan Xue, Krishan Rasiah, Nikeith John, Daniel Moon, Mark Frydenberg, John Yaxley, Phillip Stricker, Keith Wong, Geoff Coughlin, Troy Gianduzzo, Boon Kua, Bao Ho, Andrew Nguyen, Victor Liu, Jonathan Lee, Edward Hsiao, Tom Sutherland, Elisa Perry, Wolfgang P Fendler, Thomas A Hope

Department of Theranostics and Nuclear Medicine, St. Vincent's Hospital Sydney, Sydney, New South Wales, Australia; ., Garvan Institute of Medical Research, Sydney, New South Wales, Australia., Department of Theranostics and Nuclear Medicine, St. Vincent's Hospital Sydney, Sydney, New South Wales, Australia., Ahmanson Translational Theranostics, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, UCLA, Los Angeles, California., Department of Nuclear Medicine, University of Duisburg-Essen and German Cancer Consortium-University Hospital Essen, Essen, Germany., Department of Nuclear Medicine, Kantonsspital Baden, Baden, Switzerland., Department of Nuclear Medicine, School of Medicine, Technical University Munich, Munich, Germany., Department of Urology, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia., Department of Surgery, Faculty of Medicine, Monash University, Melbourne, Victoria, Australia., Department of Urology, Royal North Shore Hospital, Sydney, New South Wales, Australia., Division of Cancer Surgery, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia., Wesley Hospital, Brisbane, Queensland, Australia., St. Vincent's Prostate Cancer Centre, Darlinghurst, New South Wales, Australia., Department of Radiology, St. Vincent's Hospital Melbourne, Melbourne, Victoria, Australia; and., Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California.