Uptake of ¹⁸F-rhPSMA-7.3 in Positron Emission Tomography Imaging of Prostate Cancer: A Phase 1 Proof-of-Concept Study

Background: This study evaluated tracer uptake and lesion detectability with the novel radiopharmaceutical F-18-radiohybrid (rh)PSMA-7.3 in patients with prostate cancer (PCa).Materials and Methods: Ten patients (three with high-risk primary localized PCa [Cohort A], three with hormone-sensitive metastatic PCa [Cohort B], and four with castration-resistant metastatic PCa [Cohort C]) underwent whole-body F-18-rhPSMA-7.3 positron emission tomography (PET)/computed tomography (CT) and findings were correlated with standard-of-care imaging. F-18-rhPSMA-7.3 maximum standardized uptake value (SUVmax) and its possible association with Gleason score (GS)/International Society of Urological Pathology (ISUP) grade group (GG) and serum PSA levels were evaluated. Cohort A F-18-rhPSMA-7.3 findings were also correlated with histopathology, including prostate-specific membrane antigen (PSMA) staining.Results: F-18-rhPSMA-7.3 identified the primary tumor in 3/3 Cohort A patients and lymph node (LN) and/or bone lesions in 7/7 metastatic patients. All prostate lesions with GS >= 4 + 3/GG >= 3 were identified, but only 1/4 GS <= 3 + 4/GG <= 2 lesions. Prostate lesion SUVmax appeared positively associated with GS/GGs. Among metastatic patients, F-18-rhPSMA-7.3 identified all known pelvic and extrapelvic LN metastases and all known bone lesions. F-18-rhPSMA-7.3 detected possible additional nodal and bone lesions not reported in standard-of-care imaging in all metastatic patients. No association existed between bone or LN uptake and either GS/GG or PSA.Conclusions: F-18-rhPSMA-7.3 PET/CT showed good detection of primary and metastatic PCa lesions. In this small patient population, F-18-rhPSMA-7.3 identified intraprostatic lesions with GS >= 4 + 3/GG >= 3 with good accuracy.