Impact of Clinical Factors on 18F-rhPSMA-7.3 Detection Rates in Men with Recurrent Prostate Cancer: Findings from the Phase 3 SPOTLIGHT Study

Abstract

<h3>Purpose/Objective(s)</h3> ¹⁸F-rhPSMA-7.3 is a novel high affinity PSMA-targeting PET ligand with potential for low bladder activity. The SPOTLIGHT study (NCT04186845) evaluated ¹⁸F-rhPSMA-7.3 in men with suspected prostate cancer recurrence. Here, we report the impact of clinical factors on ¹⁸F-rhPSMA-7.3 detection rates (DR). <h3>Materials/Methods</h3> Patients underwent PET 50–70 min after IV administration of 296 MBq ¹⁸F-rhPSMA-7.3. Scans were evaluated by 3 blinded central readers. DR, including region level analyses, were stratified by baseline PSA levels, PSA doubling time (PSAdt), Gleason score (GS) and prior treatment (radical prostatectomy ± radiotherapy ["post-RP"] or radiotherapy only ["post-RT"]). <h3>Results</h3> In total, 389 men (median [range] PSA, 1.10 [0.03-135] ng/mL) had an evaluable ¹⁸F-rhPSMA-7.3 scan. The overall DR was 68–92% across the 3 readers and 83% (322/389) by majority read. Pelvic LN DR ranged from 29–36% across the 3 readers (majority read, 30%) and DR in extrapelvic sites ranged from 38–45% (majority read, 40%). In the prostate region, DR ranged from 70–98% with a majority read of 77% in the 84 patients who were post-RT and from 14–57% (majority read, 27%) in the 305 post-RP patients. The table reports DR stratified by baseline PSA. Prostate/bed and extrapelvic DR broadly increased with increasing PSA, while pelvic LN DR remained more uniform across the PSA range. PSAdt did not appear to influence DR among the 143 patients for whom PSAdt could be determined. Among post-RP patients, overall DR by majority read were 78% (25/32), 70% (23/33), 77% (17/22) and 83% (15/18) for PSAdt of <6, ≥6 – <12, ≥12 – <24 and ≥24 months, respectively. DR of 100% were noted across all PSAdt categories in post-RT patients. Among the 367 patients for whom a baseline GS was available, overall DR were uniformly high across all GS; at GS ≤6, 7, 8, 9 and 10, the DR were 89% (16/18), 76% (142/187), 86% (25/29), 83% (50/60) and 100% (1/1), respectively, in post-RP patients. In post-RT patients, DR were 100% (16/16), 98% (43/44), 100% (10/10) and 100% (2/2) at GS of ≤6, 7, 8 and 9, respectively. Although low numbers of patients in some categories limit meaningful conclusions, there was a trend towards higher prostate/bed DR at lower GS, and higher pelvic LN and extrapelvic DR at higher GS, irrespective of prior treatment. <h3>Conclusion</h3> High ¹⁸F-rhPSMA-7.3 DR were observed over a wide range of PSA, PSAdt and GS, supporting the clinical utility of ¹⁸F-rhPSMA-7.3 PET for a broad range of patients with recurrent prostate cancer.