Bone scans may overstage prostate cancer at initial staging compared with prostate-specific membrane antigen (PSMA) positron-emission tomography (PET), according to a recent study published by Hope et al in The Journal of Nuclear Medicine.
Background
PSMA PET is known to be more accurate than computed tomography (CT) and bone scans for staging patients with prostate cancer. In recent years, this strategy has become the standard imaging modality at initial staging. However, nearly all prostate cancer trials have used CT and bone scans for staging, and, consequently, the best way to apply those data to patients staged with PSMA PET remains unclear.
“Most research to date has focused on the increased sensitivity of PSMA PET vs conventional imaging such as bone scans and CT [scans],” explained lead study author Thomas Hope, MD, Vice Chair of Clinical Operations and Strategy in the Department of Radiology and Director of Molecular Therapy at the University of California, San Francisco. “In this study, my colleagues and I took the opposite approach and looked at where PSMA PET was negative when bone scans were positive,” he continued.
Study Methods and Findings
In the recent multicenter retrospective diagnostic study, investigators recruited 167 patients with prostate cancer at various disease states who were imaged with bone scans and PSMA PET within 100 days. Each study was interpreted by three blinded readers. Using PSMA PET scans as the reference standard, the investigators evaluated the positive predictive value, negative predictive value, and specificity for the bone scans as well as the interreader reproducibility, positivity rate, uptake on PSMA PET, and number of lesions.
Although the specificity of the bone scans was found to be high and similar across disease states, the positive predictive value of the bone scans at initial staging was much lower than in the overall population. When compared with PSMA PET, 57% of the bone scans at initial staging were found to contain false-positive metastases. The investigators emphasized that the significant false-positive rate of metastases on the bone scans suggested definitive therapy for local disease may have been inappropriately withheld from these patients.
Conclusions
“Rather than receiving definitive radiation treatment for localized disease, these patients may have received treatment aimed at preventing the further spread of what was incorrectly identified as metastatic disease,” underscored Dr. Hope. “These results bring into question how to apply data from clinical trials that are based on bone scans to patients who receive PSMA PET. Looking at the big picture, this study highlights the importance of understanding how test characteristics impact patient management.”
Disclosure: For full disclosures of the study authors, visit jnm.snmjournals.org.
