(UroToday.com) The 2024 American Urological Association (AUA) Annual Meeting held in San Antonio, TX between May 3rd and 6th, 2024 was host to an advanced prostate cancer podium session. Dr. Maya Ataya presented the results of an analysis evaluating the percentage of positive 68Ga-PSMA-PET/CT scans based on PSA ranges across distinct indications for the scan.
Dr. Ataya noted that serum PSA acts as a sensitive indicator for prostate cancer recurrence following curative-intent treatment. However, PSA values do not localize the location of recurrence(s). Conventional imaging (CT, bone scan, MRI) is limited by poor sensitivity and specificity at low PSA values and does not reliably identify sites of recurrence(s). Owing to its improved performance characteristics, PSMA-PET/CT is now approved for staging intermediate/high-risk patients with biochemical recurrence. In this study, Dr. Ataya and colleagues assessed the probability of a positive PSMA PET scan across PSA ranges and by prior treatment received (radical prostatectomy, radiotherapy, or both).
The investigators utilized the Indiana University-held Expanded Access IND for the clinical use of 68Ga-PSMA-PET scans for biochemically recurrent prostate cancer (2017 – 2022). They identified 815 patients, with a thorough retrospective review of the clinical history and imaging findings accordingly performed. Patients were classified into one of four biochemical recurrence groups based on the prior treatment received:
- Post-prostatectomy
- Post-radiation
- Post-prostatectomy and salvage radiation
- Stage IV
The primary outcome was the percentage of positive PSMA-PET scans across different PSA ranges in each of those four treatment-defined groups. Summarized below are the percentages of positive PSMA-PET scans by PSA range and prior therapy received. For each treatment group, Dr. Ataya highlighted the PSA range cut-off above which ≥50% of scans were positive, which may serve as a clinical reference in practice to guide imaging decision-making. As highlighted in the red boxes below, the cut-off for both post-prostatectomy and post-radiation patients was 0.51–1 ng/ml. In the post-prostatectomy + radiotherapy group, a PSA cut-off of 0.21–0.5 ng/ml portended a 63% PSMA PET positivity rate.
Next, the investigators evaluated pathologic factors that predict a positive PSMA PET scan in patients with PSA values of 0.2–0.5 and 0.5–1 ng/ml. In the 0.2–0.5 ng/ml group, a Gleason Score ≥8 and seminal vesicle invasion were significantly associated with increased odds of a positive PSMA-PET/CT. Conversely, in the 0.5-1 ng/ml group, a higher Gleason Score, extraprostatic extension, seminal vesicle invasion, and pathologic nodal involvement were all associated with increased odds of a positive scan.
Dr. Ataya concluded as follows:
- For post-prostatectomy and radiation patients, a PSA threshold of 0.5–1 ng/ml can be used to guide imaging decision-making as ≥50% of scans are positive at this threshold
- For patients who experience biochemical recurrence post-prostatectomy and radiation, the corresponding threshold is lower at 0.2–0.5 ng/ml
- For patients with stage IV disease, the majority were on ADT and thus had lower PSA values for a higher disease burden
- For all groups, as PSA values increase, so does the probability of a positive scan
Presented by: Maya Ataya, MD, Postdoctoral Researcher, Department of Urology, Indiana University, Indianapolis, IN
Written by: Rashid Sayyid, MD, MSc - Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2024 American Urological Association (AUA) Annual Meeting, San Antonio, TX, May 3rd - 6th, 2024