SNMMI 2024: 68Ga-PSMA-11 PET/CT for Baseline Staging of High-Risk Prostate Cancer: Associations Between Clinical Risk Factors, Metastases and Imaging Parameters

(UroToday.com) The Society of Nuclear Medicine & Molecular Imaging (SNMMI) 2024 Annual Meeting held in Toronto, ON between June 8^th and June 11^th, 2024 was host to a prostate cancer imaging session. Dr. Gary Cook discussed the associations between clinical risk factors, metastases, and imaging parameters for patients with high-risk prostate cancer undergoing baseline staging with ⁶⁸Ga-PSMA-11 PET/CT.

The PSMA PET service at the King’s College London & Guy’s and St Thomas’ PET Centre was initiated in 2017 with [⁶⁸Ga]THP-PSMA initially and subsequently changed to [⁶⁸Ga]PSMA-11 in February 2020. All patients with a new diagnosis of intermediate to high-risk prostate cancer (PSA >20, ISUP >3 or cT stage T3a) are eligible for [⁶⁸Ga]PSMA-11 PET/CT staging at this center. Subsequent prospective evidence from the proPSMA trial confirmed improved accuracy compared to conventional imaging.¹ The objective of this study was to review this center’s practice data to determine the number of patients with metastatic disease and to explore relationships between clinical risk factors and primary tumour SUVmax.

This was a real world, single center, retrospective analysis of consecutive [⁶⁸Ga]PSMA PET/CT scans in all intermediate to high-risk, newly diagnosed prostate cancer patients from February 2020 to April 2023. The following data variables were collected:

• PSMA PET presence of N or M status
• SUV_max of the primary prostate lesion
• MRI T-stage
• Gleason/ISUP score
• PSA
• Age
• Primary treatment modality
• Presence/absence of biochemical recurrence during follow-up

The study cohort included a total 525 evaluable subjects, of whom 146 (28%) underwent a robot-assisted radical prostatectomy and 379 (72%) were treated non-surgically.

The baseline patient characteristics are summarized below:

Of the 525 patients who were imaged, 116 (22.1%) had evidence of metastatic disease:

As demonstrated below, patients with a higher ISUP grade score had a higher mean SUV_max expression on PSMA-PET/CT:

The clinicopathologic variables that were significantly associated with an increased risk of metastasis were as follows:

• PSA ≥20 ng/ml: 4.5% risk
• Stage ≥cT3: 13.3%
• ISUP Grade ≥3: 10%
  • ISUP 3: 7.5%
  • ISUP 4: 6.7%
  • ISUP 5: 17.6% 

The metastatic risk by the number of factors present was as follows:

• 1 risk factor: 11.8%
• 2 risk factors: 25.6%
• 3 risk factors: 43.5%

There was no association between SUV_max and biochemical recurrence risk.

Dr. Cook concluded as follows:

• Serum PSA ≥20 ng/ml, ISUP ≥3 , and ≥cT3a disease are associated with increased risk of metastases.
• Overall 22.1% of patients have evidence of metastatic disease on PSMA-PET/CT
• The risk increases with the number of risk factors (43.5% if all risk factors are present)
• SUV_max correlates with markers of disease severity (e.g., ISUP grade), but not biochemical recurrence

Presented by: Gary J. Cook, MD, Professor of PET Imaging, King’s College London, London, UK

Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the Society of Nuclear Medicine & Molecular Imaging (SNMMI) 2024 Annual Meeting held in Toronto, ON between June 8^th and June 11^th, 2024

1. Hofman MS, Lawrentschuk N, Francis RJ, et al. Prostate-specific membrane antigen PET-CT in patients with high-risk prostate cancer before curative-intent surgery or radiotherapy (proPSMA): a prospective, randomised, multicentre study. Lancet. 2020;395(10231):1208-1216.