(UroToday.com) The Society of Nuclear Medicine & Molecular Imaging (SNMMI) 2024 Annual Meeting held in Toronto, ON between June 8th and June 11th, 2024 was host to a prostate cancer imaging session. Dr. Francisco Osvaldo García-Pérez presented an analysis of the use of 18F-PSMA-1007 PET /CT for the evaluation of atypical patterns of spread in ISUP Grade Group 5 prostate cancer.
Dr. García-Pérez noted that patients with ISUP Grade Group 5 disease may have atypical dissemination patterns secondary to the underlying aggressive biology that may make the diagnostic/staging work up challenging in this setting. Novel PET imaging techniques may offer an advantage in this setting owing to their improved performance characteristics. The objective of this study was to describe atypical dissemination patterns detected by 18F-PSMA-1007 PET/CT that had subsequent lesion confirmation by immunohistochemistry with NKX3.1, a highly sensitive and specific marker for prostatic cell clonal origin in high-grade metastatic tumors.
This was a retrospective analysis of 86 consecutive patients with biopsy proven Grade Group 5 disease (i.e., Gleason Score 9–10) who underwent both a staging and re-staging 18F-PSMA-1007 PET/CT between 2017 and 2022 at a single institution. PSA values were correlated with the total tumor burden using Pearson’s Correlation Index. A comparison of the mean SUVmax between mixed and pure histology lesions was performed using the Mann-Whitney U test.
Thirty-five patients (mean age: 56.4 years) with atypical sites of metastases (n=41) and who had prostate cancer disease origin confirmed using NKX3.1 histopathologic/immunohistochemistry were identified. The most common sites of metastases are summarized in the table below:
The 18F PSMA-1007 PET-positive lesions had a median SUVmax of 4.1 (range: 1.8–31.1) The mean PSA value at diagnosis was 35.4 ng/ml (range: 8.9 –78.1 ng/ml). PSA levels at imaging were not significantly correlated with PSMA total tumor volume (r=0.456, p=0.12). In 63% of patients (22/35), note was made of co-existence of other histologies, including:
- Neuroendocrine histologies (n=4 small cells, n=3 large cells)
- Intestinal phenotype, n=7
- Prostatic ductal, n=5
- Mucinous (excluding intestinal phenotype), n=3.
The mean SUVmax of mixed histology lesions was lower than that of pure histology lesions (mean: 4.4 +/- 3.3 versus 8.9 +/- 9.9; p=0.069).
Dr. García-Pérez concluded that in patients with Grade Group 5 disease, 18F PSMA-1007 PET/CT uptake values are variable, potentially owing to underlying variant histology differentiation, and the sites of dissemination may not follow a conventional spread pattern. Additionally PSA values at imaging did not significantly correlate with PSMA total tumor volume, suggesting that reliance on PSA alone in this setting may be inadequate.
Presented by: Francisco Osvaldo O. García-Pérez, MD, Nuclear Medicine & Molecular Imaging, Instituto Nacional de Cancerología, Universidad Nacional Autónoma de México, Mexico City, Mexico
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 Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, Fri, May 31 – Tues, June 4, 2024.