Histologically Confirmed Diagnostic Efficacy of 18F-rhPSMA-7 PET for N-Staging of Patients with Primary High-Risk Prostate Cancer

Abstract

18F-rhPSMA-7 (radiohybrid prostate-specific membrane antigen [PSMA]) is a novel ligand for PET imaging. Here, we present data from a retrospective analysis using PET/CT and PET/MRI examinations to investigate the efficacy of 18F-rhPSMA-7 PET for primary N-staging of patients with prostate cancer (PC) compared with morphologic imaging (CT or MRI) and validated by histopathology. Methods: Data from 58 patients with high-risk PC (according to the D'Amico criteria) who were staged with 18F-rhPSMA-7 PET/CT or PET/MRI at our institution between July 2017 and June 2018 were reviewed. The patients had a median prescan prostate-specific antigen value of 12.2 ng/mL (range, 1.2-81.6 ng/mL). The median injected activity of 18F-rhPSMA-7 was 327 MBq (range, 132-410 MBq), with a median uptake time of 79.5 min (range, 60-153 min). All patients underwent subsequent radical prostatectomy and extended pelvic lymph node dissection. The presence of lymph node metastases was determined by an experienced reader independently for both the PET and the morphologic datasets using a template-based analysis on a 5-point scale. Patient-level and template-based results were both compared with histopathologic findings. Results: Lymph node metastases were present in 18 patients (31.0%) and were located in 52 of 375 templates (13.9%). Receiver-operating-characteristic analyses showed 18F-rhPSMA-7 PET to perform significantly better than morphologic imaging on both patient-based and template-based analyses (areas under curve, 0.858 vs. 0.649 [P = 0.012] and 0.765 vs. 0.589 [P < 0.001], respectively). On patient-based analyses, the sensitivity, specificity, and accuracy of 18F-rhPSMA-7 PET were 72.2%, 92.5%, and 86.2%, respectively, and those of morphologic imaging were 50.0%, 72.5%, and 65.5%, respectively. On template-based analyses, the sensitivity, specificity, and accuracy of 18F-rhPSMA-7 PET were 53.8%, 96.9%, and 90.9%, respectively, and those of morphologic imaging were 9.6%, 95.0%, and 83.2%, respectively. Conclusion:18F-rhPSMA-7 PET is superior to morphologic imaging for N-staging of high-risk primary PC. The efficacy of 18F-rhPSMA-7 is similar to published data for 68Ga-PSMA-11.

Keywords: N-staging; PET; hybrid imaging; lymph nodes; prostate cancer; prostate-specific membrane antigen (PSMA).

© 2020 by the Society of Nuclear Medicine and Molecular Imaging.

Figures

FIGURE 1.

Flowchart for patient selection.

FIGURE 2.

ROC curves for 18F-rhPSMA-7 PET and morphologic imaging (MRI/CT) for primary lymph node staging of prostate cancer in patient-based analysis (A) and template-based analysis (B). Comparison to AUC of 0.5 is indicated by gray line.

FIGURE 3.

Set of images from 71-y-old patient (Gleason score of 10, initial prostate-specific antigen level of 1.15 ng/mL). (A) Whole-body maximum-intensity projection displays local tumor and 1 suspected lesion (arrow). Local tumor is not detectable on CT (B) but shows increased tracer uptake on 18F-rhPSMA-7 PET (D) and PET/CT (F). CT (E) reveals suggestive finding (arrow), with 8-mm lymph node ventral to left external iliac vein; corresponding 18F-rhPSMA-7 PET (E) and PET/CT images (G) show intense uptake with high lesion-to-background ratio in this small lymph node, indicating lymph node metastasis. Radical prostatectomy with extended pelvic lymph node dissection confirmed single lymph node metastasis.