(UroToday.com) PSMA is a transmembrane glycoprotein with folate hydrolase activity. It is very specific in differentiating benign and malignant prostate cells. It has been shown to be overexpressed in prostate cancer cells, and especially in metastatic and castrate-resistant disease. Prostate-specific membrane antigen (PSMA) is expressed 100 to 1,000 times more highly in prostatic adenocarcinoma than in benign prostate tissue, particularly in the setting of androgen deprivation. Around the world, there is a significant rapid adoption of PSMA PET-CT/MRI, which can detect metastatic disease that is inapparent on conventional imaging (CT and bone scintigraphy).
In the presented prospective multicenter single-arm open-label phase 3 imaging trial (NCT03368547, NCT02611882, NCT2919111), the authors aimed to determine the accuracy of 68-GA-PSMA-11 PET for the detection of pelvic nodal metastasis (N1) compared to histopathology at time of radical prostatectomy (RP).
The study took place at the University of California, Los Angeles (UCLA) and at San Francisco (UCSF) between December 2015 to August 2019. A total of 633 patients were imaged, and more than 277 patients underwent radical prostatectomy. All patients hand intermediate to high-risk prostate cancer according to the D’Amico risk classification. Patients were injected with 3-7 mCi of 68Ga-PSMA-11 and imaged with either PET/CT or PET/MRI. The imaging took place approximately 50 to 100 minutes following injection.
The authors compared imaging results to final pathology results after prostatectomy using three blinded readers with no clinical data available at the time of interpretation. The surgery patient population is shown in table 1, and the sensitivity and specificity results are shown in Table 2, demonstrating a sensitivity of 40% and specificity of 95% for PSMA PET. The stratified results by PSA and Gleason score are shown in table 3, showing a sensitivity of 0.47 and 0.43 for PSA>=11 and Gleason score of 8-10, respectively. In contrast, for PSA <11 and Gleason score of 6-7, the sensitivity was 0.30 and 0.33, respectively. The authors also looked at the impact of the lymph node size. They demonstrated that for a lymph node measuring 1 centimeter or less, the sensitivity was 0.29. However, for a lymph node measuring more than one centimeter, the sensitivity was markedly increased at a level of 0.59. The authors found that 87% of patients with true positive disease (20/23) on PSMA PET had biochemical recurrence after prostatectomy.
In summary, the results of this prospective trial evaluating the role of PSMA PET demonstrated a sensitivity of 40% and specificity of 95%. Patients with larger nodes, higher preoperative PSA, and higher Gleason score had increased sensitivities. Lastly, 87% of patients with true positive disease had a biochemical recurrence following surgery. The authors concluded that optimal management based on PSMA PET results has yet to be determined.
Presented by: Thomas Hope, MD, Associate Professor, Department of Radiology and Biomedical Imaging, University of California, San Francisco
Written by: Hanan Goldberg, MD, MSc., Urology Department, SUNY Upstate Medical University, Syracuse, NY, USA @GoldbergHanan at the 2020 ASCO Annual Meeting, Virtual Scientific Program #ASCO20, May 29- 31, 2020
Watch: 68Ga-PSMA PET: A Novel Imaging Technique Prior to Radical Prostatectomy in Men with Intermediate or High Risk Prostate Cancer - Thomas Hope