Normal-organ distribution of PSMA-targeting PET radiopharmaceutical F-flotufolastat: a post hoc analysis of the LIGHTHOUSE and SPOTLIGHT studies.

Background: High-affinity radiohybrid PSMA-targeting radiopharmaceutical F-flotufolastat (F-rhPSMA-7.3) is newly approved for diagnostic imaging of prostate cancer. Here, we conduct a post hoc analysis of two phase 3 studies to quantify F-flotufolastat uptake in a range of normal organs.

Methods: All 718 evaluable F-flotufolastat scans from LIGHTHOUSE and SPOTLIGHT were re-evaluated. Additionally, patients' medical records were reviewed and any patients with high tumor burden (PSA>20 ng/mL), altered biodistribution (e.g., chronic kidney disease), major anatomical changes to normal organs (e.g., nephrectomy), or any other history of cancer were excluded. A medical physicist defined volumes of interest over specific organs for evaluation of SUV and SUV per PERCIST 1.0 criteria. Normally distributed data are reported as mean (SD) and non-normally distributed data as median (IQR). The co-efficient of variation (CoV; calculated as SD/mean for normally distributed data and IQR/median for non-normally distributed data) was used to quantify variability of SUV metrics.

Results: In total, scans from 546 patients (244 primary, 302 recurrent) were eligible for this analysis. All organs were considered to be normally distributed except for the bladder and spleen. In the liver, the mean SUV was 6.7 (SD 1.7), CoV 26%, while the bladder median SUV was 10.6 (IQR 11.9), CoV 112%. The mean SUV in the liver was 8.2 (SD 2.1), CoV 26% and median SUV in the bladder was 16.0 (IQR 18.5), CoV 116%.

Conclusions: Physiological F-flotufolastat uptake in normal organs was broadly consistent with other renally-cleared radiopharmaceuticals, which may have clinically significant implications when considering patient selection for radioligand therapy. Additionally, the bladder median SUV for F-flotufolastat was lower than that previously reported for Ga-PSMA-11 and F-DCFPyL.