PSMA-PET may provide optimal disease staging for some prostate cancer patients

A recent article in the Journal of Nuclear Medicine reports findings of a multi-center retrospective study that compares bone scan with PSMA PET for initial staging of prostate cancer. Authors include UCSF Radiology and Biomedical Imaging faculty members Thomas Hope, MD, Roxanna Juarez, MD, Miguel Hernandez Pampaloni, MD, PhD, and clinical research coordinator Daniel Thompson. Co-authors are Matthias Benz, Martin Allen-Auerbach, Pawan Gupta, and senior author Jeremie Calais of UCLA; Fei Jiang of UCSF Epidemiology and Biostatistics; and Francesco Barbato and Wolfgang P. Fendler of the University of Duisburg–Essen.

Titled "Do Bone Scans Overstage Disease Compared with PSMA PET at Initial Staging? An International Multicenter Retrospective Study with Masked Independent Readers," the purpose of the study was to improve our understanding of how to apply clinical trial data based on conventional imaging to patients staged using PSMA PET. To do this, the researchers evaluated the ability of bone scans to detect osseous metastases using PSMA PET as a reference standard. Regarding potential improvements to patient care, overstaging for metastasis – when local disease is a more accurate diagnosis – may subject patients to treatments that increase therapy-related morbidity.

The study included 167 patients with prostate cancer, who were imaged with bone scans and PSMA PET performed within 100 days of one another to compare interpretations of the bone scans at various stages of disease, using the results of the PSMA PET as a reference standard.

In a recent post on Twitter/X, Dr. Hope noted, "If you thought PSMA PET always led to stage migration, you might want to think again. At initial staging over half of patients with bone mets on bone scan were negative on PSMA PET. Sometimes increased accuracy leads to fewer mets!" His tweet has more than 77,000 views to date.

The authors summarize the study's conclusions: "In this multicenter retrospective diagnostic study using PSMA PET as the reference standard, the positive predictive value (PPV) of bone scans at initial staging was low (0.43). This results in incorrect staging (as having osseous metastasis) of more than half of patients in this group. This overstaging by bone scans is important when applying clinical data from trials such as the STAMPEDE M1 RT trial to patients being staged with PSMA PET. Before patients receive prostate bed RT in low-volume metastatic disease on PSMA PET, further work should be performed to understand if the results of the STAMPEDE M1 RT trial are generalizable."