Normal-organ distribution of PSMA-targeting PET radiopharmaceutical 18F-flotufolastat: a post hoc analysis of the LIGHTHOUSE and SPOTLIGHT studies.

Abstract

High-affinity radiohybrid PSMA-targeting radiopharmaceutical 18F-flotufolastat (18F-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 18F-flotufolastat uptake in a range of normal organs. All 718 evaluable 18F-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 SUVmean and SUVpeak 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. 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 SUVmean was 6.7 (SD 1.7), CoV 26%, while the bladder median SUVmean was 10.6 (IQR 11.9), CoV 112%. The mean SUVpeak in the liver was 8.2 (SD 2.1), CoV 26% and median SUVpeak in the bladder was 16.0 (IQR 18.5), CoV 116%. Physiological 18F-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 SUVpeak for 18F-flotufolastat was lower than that previously reported for 68Ga-PSMA-11 and 18F-DCFPyL.