Impact of Clinical Factors on 18F-Flotufolastat Detection Rates in Men With Recurrent Prostate Cancer: Exploratory Analysis of the Phase 3 SPOTLIGHT Study

Purpose

¹⁸F-Flotufolastat (¹⁸F-rhPSMA-7.3) is a newly approved prostate-specific membrane antigen targeting radiopharmaceutical for diagnostic imaging of prostate cancer (PCa). SPOTLIGHT (National Clinical Trials 04186845) evaluated ¹⁸F-flotufolastat in men with suspected PCa recurrence. Here, we present results of predefined exploratory endpoints from SPOTLIGHT to evaluate the impact of clinical factors on ¹⁸F-flotufolastat detection rates (DR).

Methods and Materials

The impact of baseline prostate-specific antigen (PSA), PSA doubling time (PSAdt), and International Society of Urologic Pathology Grade Group (GG) on ¹⁸F-flotufolastat DR was evaluated among all SPOTLIGHT patients with an evaluable scan, with DR stratified according to the patients’ prior treatment (radical prostatectomy ± radiation therapy [RP] or radiation therapy only [RT]). The patients underwent positron emission tomography 50 to 70 minutes after receiving ¹⁸F-flotufolastat (296 MBq IV), and scans were read by 3 blinded central readers, with the majority read representing agreement between ≥2 readers.

Results

In total, 389 men (median PSA: 1.10 ng/mL) were evaluable. By majority read, ¹⁸F-flotufolastat identified distant lesions in 39% and 43% of patients treated with prior RP or RT, respectively. The overall DR broadly increased with increasing PSA (<0.2 ng/mL: 33%; ≥10 ng/mL: 100%). Among patients with PSA <1 ng/mL, 68% had positive scans, and 27% had extrapelvic findings. PSAdt was available for 145/389 (37%) patients. PSAdt did not appear to influence ¹⁸F-flotufolastat DR (77%-90% across all PSAdt categories). Among patients with prior RP, DR ranged from 70% to 83% across PSAdt categories, and 100% DR was reported for all post-RT patients. In total, 362/389 (93%) patients had baseline GG data. Overall DRs were uniformly high (75%‒95%) across all GG. When stratified by prior treatment, DRs across all GG were 69% to 89% in patients with prior RP and ≥96% in patients with prior RT.

Conclusions

¹⁸F-Flotufolastat-positron emission tomography enabled the accurate detection of recurrent PCa lesions across a wide range of PSA, PSAdt, and International Society of Urologic Pathology GG, thus supporting its clinical utility for a broad range of patients with recurrent PCa.