Diagnostic Utility of rhPSMA-7.3 (18F) PET/CT in Men With Prostate Cancer on Active Surveillance

This investigator-initiated, single-center, prospective study aims to evaluate the diagnostic utility of rhPSMA-7.3 (¹⁸F) PET/CT (flotufolastat F18, marketed as POSLUMA®) in detecting clinically significant prostate cancer (csPCa) among men on active surveillance for low-risk or favorable intermediate-risk prostate cancer.

Background and Rationale: Active surveillance (AS) is the preferred management strategy for carefully selected men with low-risk and favorable intermediate-risk prostate cancer, balancing the avoidance of overtreatment against the need to identify disease progression early. Current surveillance strategies rely on serial PSA monitoring, digital rectal examination, mpMRI, and confirmatory biopsies. However, mpMRI can miss or underestimate clinically significant lesions, particularly those in the anterior or transitional zones. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells and can be visualized using PET/CT imaging with radiolabeled PSMA ligands. The next-generation tracer rhPSMA-7.3 (¹⁸F), or flotufolastat F18, has demonstrated improved image resolution, favorable kinetics, and low urinary excretion compared to earlier PSMA ligands. Incorporating PSMA PET/CT into the active surveillance pathway may identify occult or higher-grade disease not detected by MRI, improving risk stratification and treatment decision-making.

Study Objectives: The primary objective of the study is to determine whether the addition of rhPSMA-7.3 (¹⁸F) PET/CT to standard mpMRI improves detection of clinically significant prostate cancer (ISUP Grade Group ≥2) in men on active surveillance.

Secondary objectives include: Comparing lesion-level concordance between PET/CT, mpMRI, and histopathology. Evaluating the predictive value of PET SUVmax for detecting clinically significant disease. Assessing diagnostic performance metrics (sensitivity, specificity, PPV, NPV) for PET/CT versus MRI. Quantifying the proportion of patients reclassified (i.e., upgraded or transitioned from AS to definitive treatment) based on PET/CT findings.

Exploratory endpoints include: Association between PET quantitative parameters (SUVmax, lesion volume) and PSA density. Characterization of PET-only lesions not visualized on MRI. Correlation of PET/CT findings with adverse pathological features (ECE, SVI, cribriform/intraductal carcinoma) at biopsy or surgery. Evaluation of lesion-level changes in SUVmax and volume in patients who undergo repeat PET/CT.

Study Design: This is a prospective, single-arm diagnostic utility study. Approximately 120 participants with histologically confirmed low-risk or favorable intermediate-risk prostate cancer managed with active surveillance will be enrolled at Mount Sinai Hospital. All participants will undergo both mpMRI and rhPSMA-7.3 (¹⁸F) PET/CT prior to confirmatory biopsy. Imaging data will be reviewed by genitourinary radiologists and nuclear medicine physicians blinded to each other's findings. Lesions will be recorded according to standardized templates (e.g., PIRADS 2.1 for MRI and SUV-based mapping for PET/CT). Targeted biopsies will include MRI-positive, PET-positive, and fusion (concordant) targets, as well as systematic cores as per institutional protocol. Histopathology will serve as the reference standard for correlation. The study involves one PET/CT visit, one confirmatory biopsy, and up to three follow-up visits within 12 months.

Risks and Benefits: Risks include exposure to low-dose radiation comparable to standard diagnostic imaging, and expected biopsy-related discomfort such as pain, bleeding, infection, or transient urinary symptoms. Rare allergic reactions to flotufolastat F18 and mild emotional stress associated with imaging or awaiting results are possible but uncommon. There may be no direct benefit to participants. However, rhPSMA-7.3 (¹⁸F) PET/CT may help identify previously undetected higher-grade disease, leading to earlier or more appropriate treatment. The findings could improve future management of men on active surveillance.

Statistical Considerations: Diagnostic accuracy metrics will be analyzed at both lesion and patient levels using confirmatory biopsy as the gold standard. ROC analysis will determine SUVmax thresholds for predicting clinically significant disease. Concordance between PET and MRI findings will be evaluated with Cohen's kappa and McNemar's test. Sample size (n=120) is based on expected detection differences between PET/CT and MRI with 80% power and alpha=0.05.

Study Oversight: This study is conducted under the oversight of the Mount Sinai Program for the Protection of Human Subjects (PPHS) and complies with FDA regulations for IND-exempt studies involving FDA-approved radiopharmaceuticals (21 CFR 312.2(b)(1)). The study is jointly funded by the Icahn School of Medicine at Mount Sinai and Blue Earth Diagnostics. Mount Sinai is the study sponsor and holds regulatory responsibility. Blue Earth Diagnostics provides the imaging agent flotufolastat F18 (POSLUMA®), technical support, and partial financial support. Data management and analysis will be conducted internally at Mount Sinai. No external contract research organization (CRO) or vendor (e.g., Parexel) will manage study data.

Expected Duration: Enrollment start: November 2025 Primary completion: May 2027 (final confirmatory biopsy) Study completion: November 2027 (data lock and analysis)

Potential Impact: This study may validate the clinical role of rhPSMA-7.3 (¹⁸F) PET/CT in improving detection of clinically significant prostate cancer during active surveillance. The results may support integration of PSMA-targeted PET imaging into future diagnostic pathways, minimizing unnecessary biopsies and improving individualized management.