3220 - Impact of Clinical Factors on 18 F-Piflufolastat and 18 F-Flotufolastat Detection Rates in Patients with Recurrent Prostate Cancer Post-Prostatectomy: Results from an Intra-Patient Head-to-Head Study

Purpose/Objective(s):

Prostate-specific membrane antigen (PSMA)-targeted PET has become the mainstay of prostate cancer imaging. BED-PSMA-411 (NCT06604442) was the first intra-patient head-to-head comparator study of two ¹⁸F-labeled PSMA-PET radiopharmaceuticals, ¹⁸F-piflufolastat and ¹⁸F-flotufolastat, in patients with biochemical recurrence (BCR) of prostate cancer. Here, we report the impact of clinical factors on ¹⁸F-piflufolastat and ¹⁸F-flotufolastat detection rates (DR).

Materials/Methods:

Men =18 years with low PSA (=0.5 ng/mL) BCR of prostate cancer =6 months after radical prostatectomy (RP) with undetectable PSA post-surgery were enrolled. Patients underwent PET 60 min after IV administration of 333 MBq ¹⁸F-piflufolastat. After 1–10 days, the patients had a second PET on the same scanner, 60 min after receiving IV ¹⁸F-flotufolastat (296 MBq). Images were interpreted by two blinded central readers, with a third to resolve disagreements, allowing majority read results (reported throughout). DR were stratified by baseline PSA, time since RP, initial disease stage, and ISUP Grade Group (GG).

Results:

In total, 55 men (median PSA, 0.28 ng/mL) had evaluable scans with both radiopharmaceuticals.

The overall patient-level DR was 27% (15/55) for ¹⁸F-piflufolastat and 45% (25/55) for ¹⁸F-flotufolastat. Although low numbers of patients in some categories limit practice-changing conclusions, ¹⁸F-flotufolastat showed higher overall DR in every PSA stratification from as low as =0.1 ng/mL (table). In the prostate bed, the DR was 14% (3/21) for both ¹⁸F-piflufolastat and ¹⁸F-flotufolastat at PSA =0.2 ng/mL, and 8.8% (3/34) and 21% (7/34), respectively, at PSA >0.2–0.5 ng/mL.

DR were highest among the patients with <5 years between RP and BCR (31% [13/42] for ¹⁸F-piflufolastat and 50% [21/42] for ¹⁸F-flotufolastat) compared with those with =5 years between RP and BCR (15% [2/13] for ¹⁸F-piflufolastat and 31% [4/13] for ¹⁸F-flotufolastat).

DR for ¹⁸F-piflufolastat and ¹⁸F-flotufolastat were 21% (6/28) and 43% (12/28), respectively, among patients who were N0 at initial diagnosis, and 0% (0/2) and 50% (1/2) for patients who were N1. DR for both radiopharmaceuticals increased with increasing ISUP GG. The DR was 0% (0/3) for both ¹⁸F-piflufolastat and ¹⁸F-flotufolastat for ISUP GG 1, 28% (11/39) and 46% (18/39), respectively, for GG 2–3, and 31% (4/13) and 54% (7/13) for GG 4–5.

Conclusion:

This intra-patient comparator study demonstrates the suitability of both ¹⁸F-piflufolastat and ¹⁸F-flotufolastat PET for imaging a broad range of patients with BCR of prostate cancer, with ¹⁸F-flotufolastat consistently offering higher DR among this low PSA population.

PSA, ng/mL	n	18F-Piflufolastat DR, %	18F-Flotufolastat DR, %
=0.1	2	0	100
>0.1–0.2	19	42	47
>0.2–0.3	16	25	44
>0.3–0.4	13	23	31
>0.4–0.5	5	0	60