SPOTLIGHT: Detection Rates of 18F-rhPSMA-7.3 in Patients With Low to Very Low PSA Levels

The phase 3 SPOTLIGHT study evaluated the efficacy of ¹⁸F-rhPSMA-7.3, a novel, high-affinity prostate-specific membrane antigen (PSMA)-targeting ligand with potential for low bladder activity, in patients with suspected prostate cancer recurrence. Findings from a post hoc analysis of the study, which  determined the ¹⁸F-rhPSMA-7.3 detection rates (DRs) at low to very low prostate-specific antigen (PSA) levels, were presented at the American Society for Radiation Oncology 2023 Annual Meeting.

A total of 389 patients (median [range] PSA, 1.10 [0.03-135] ng/mL; 84 with intact prostate) were involved in the study and had an evaluable ¹⁸F-rhPSMA-7.3 scan. Patients were administered positron emission tomography (PET) 50 to 70 minutes after intravenous administration of ¹⁸F-rhPSMA-7.3 296 MBq.

Scans were evaluated by 3 blinded central readers, with the majority read representing agreement between at least 2 independent readers. Overall (patient-level) and regional DRs by majority read were determined and stratified according to baseline PSA level (<0.2, 0.2 to <0.3, 0.3 to <0.5, and 0.5 to <1 ng/mL).

The overall DR was 83% (322/389) by majority read. Of the 389 eligible patients, 188 had a baseline PSA <1 ng/mL and were eligible for the present analysis. Moderate to high DRs were observed despite low patient numbers in some PSA categories. The patient-level DR was shown to increase with increasing baseline PSA.

Overall, 68% (128/188) of patients with a PSA <1 ng/mL and 64% (77/121) of patients with a PSA <0.5 ng/mL had a positive ¹⁸F-rhPSMA-7.3 scan by majority read. Regional DRs were broadly consistent across all PSA categories. Extrapelvic lesions were observed in 21% (25/121) of patients with a PSA <0.5 ng/mL and 27% (51/188) of patients with a PSA <1 ng/mL.

Among this cohort of patients with low to very low PSA levels, more than two-thirds had positive ¹⁸F-rhPSMA-7.3 scans. Over a quarter of patients had extrapelvic findings.

¹⁸F-rhPSMA-7.3 PET may serve as a useful tool for treatment planning in patients with early biochemical recurrence of prostate cancer where curative salvage therapy is of prime consideration.