Histologically-confirmed diagnostic efficacy of ¹⁸F-rhPSMA-7 positron emission tomography for N-staging of patients with high risk primary prostate cancer

Objectives: ¹⁸F-rhPSMA-7 is a new PSMA-targeting agent which can be efficiently labeled with ¹⁸F and radiometals and is associated with only minimal renal excretion. Here, we preset the results of a retrospective analysis of the efficacy of ¹⁸F-rhPSMA-7 positron emission tomography (PET) for primary N-staging compared with morphological imaging (computed tomography [CT] or magnetic resonance imaging [MRI]) and validated by histopathology. Methods: Data from patients with high risk prostate cancer (defined by D’Amico) who were staged with ¹⁸F-rhPSMA-7 PET/CT or PET/MRI at our institutions between July 2017 and June 2018 were reviewed. 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 morphological datasets, using a template-based analysis on a 5-point scale. Patient-level and template-based results were both compared to histopathological findings.

Results: Data from 58 patients were reviewed. The patients had a median pre-scan PSA of 12.4 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). Lymph node metastases were present in 18 patients (31.0%) located in 52 of 375 templates (13.9%). On patient-based analyses the sensitivity, specificity and accuracy of ¹⁸F-rhPSMA-7 PET were 72.2%, 92.5% and 86.2%, and those of morphological imaging 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 morphological imaging were 9.6%, 95.0% and 83.2%, respectively. ROC analyses showed ¹⁸F-rhPSMA-7 PET to perform significantly better than morphological imaging on both patient and template-based analyses (AUCs of 0.858 vs. 0.649, p=0.012 and 0.765 vs. 0.589, p<0.001, respectively). The histopathology revealed the median size of lymph node metastases in ¹⁸F-rhPSMA-7 negative templates to be 3.5 mm (range: 0.3-15 mm).

Conclusions: ¹⁸F-rhPSMA-7 PET is superior to morphological imaging for N-staging of high risk primary prostate cancer. The efficacy of ¹⁸F-rhPSMA-7 is similar to published data for other PSMA-ligands.