ASCO 2023: Do Bone Scans Over-Stage Disease Compared to PSMA PET? an International Multicenter Retrospective Study with Blinded Independent Readers

( The 2023 American Society of Clinical Oncology (ASCO) annual meeting held in Chicago, IL between June 2nd and June 6th was host to a prostate, testicular, and penile cancers poster discussion session. Dr. Wolfgang Fendler presented the results of an international, multicenter retrospective study evaluating whether bone scans over-stage metastatic burden, compared to PSMA-PET/CT, using blinded independent readers.

While it has been demonstrated that PSMA-PET/CT has improved diagnostic performance characteristics compared to conventional imaging with computed tomography and/or bone scans, current treatment paradigms are based on studies of patients staged via conventional imaging techniques. Accordingly, applying the results of such studies to contemporary cohorts staged via PSMA-PET/CT remains challenging. Further studies evaluating the concordance/discordance of conventional and PSMA-PET imaging findings are needed to further clarify appropriate management in this space. The objective of this study was to evaluate the ability of bone scans to detect bone metastases using PSMA-PET as the reference standard.

This was a retrospective analysis of 167 prostate cancer patients who underwent both a bone scan and PSMA-PET within 100 days at three centers (UCSF, UCLA, University Hospital Essen). Patients did not receive any new interval therapy in the period between the two imaging modalities being performed, and patients were included across the disease spectrum (initial diagnosis, biochemical recurrence, castrate sensitive or resistant prostate cancer). Each study was independently read by three blinded readers, and the results of the PSMA-PET served as the reference standard. For bone scans, the presence of metastases was recorded for 17 osseous regions. For PSMA-PETs additional TNM staging was performed.


ASCO 2023 Fendler_Bone Scans_0 

With PSMA-PET as reference standard, the authors evaluated the positive predictive value (PPV), negative predictive value (NPV), and specificity for bone scans. Additionally, inter-reader reproducibility, positivity rate, uptake on PSMA-PET, and number of lesions were evaluated.

This analysis included 167 patients, with 77 at initial staging, 60 in the biochemical recurrence/castrate-sensitive setting, and 30 in the castrate-resistant setting.

ASCO 2023 Fendler_Bone Scans_1 

The performance characteristics of bone scans were as follows:

  • PPV: 73%
  • NPV: 82%
  • Specificity: 82%

Next, the authors focused on the 77 patients at initial staging. Of these 77 patients, 13 (17%) had M1b disease on PSMA-PET, whereas 23 (30%) were M1b on bone scan. Of the 23 patients with a positive bone scan, only 10 were positive on PSMA-PET, meaning that 13/23 (57%) of positive bone scans were false-positives. In this setting, the performance characteristics for bone scan was as follows:

  • PPV: 43%
  • NPV: 94%
  • Specificity: 80%

The inter-reader agreement was moderate for bone scans (Fleiss Kappa=0.51) and substantial for the PSMA-PET reference standard (Fleiss Kappa=0.80).

Dr. Fendler concluded that in this multicenter retrospective study, the PPV of bone scans was low in patients at initial staging, with the majority of positive bone scans being false positives (57%). This suggests that a large proportion of patients considered low volume metastatic by bone scan actually have localized disease.

Presented by: Wolfgang P. Fendler, MD, Department of Nuclear Medicine, West German Cancer Center, University Hospital Essen, University of Duisburg-Essen

Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, Fri, June 2 – Tues, June 6, 2023.