Detection efficacy of PSMA-targeted PET/CT with¹⁸F-FSU880 in patients with biochemical recurrence of prostate cancer

Objectives: Recently, prostate-specific membrane antigen (PSMA) has received attention as a target of imaging and therapy for prostate cancer. We have developed a new ¹⁸F-labeled PSMA-targeting compound ¹⁸F-FSU880 and we have confirmed that PET/CT with ¹⁸F-FSU880 can be safely carried out . The aim of this study was to investigate the efficacy of PET/CT with ¹⁸F-FSU880 for detection of recurrent disease in biochemical recurrence after curative treatment.

Methods: Forty-six patients (56 - 82 yr., mean 71 yr.) who were referred for PET/CT with ¹⁸F-FSU880 for detection of biochemical recurrence (PSA≥ 0.2) after curative treatment between February 2019 and December 2020 were retrospectively assessed. Prior primary local therapy consisted of radical prostatectomy (RP) (n = 22) or radiotherapy (RT) (n = 24). The median PSA level was 2.18 ng/ml (range 0.25 - 30.19 ng/ml). Whole body PET/CT images were acquired at 1h and 3h after iv injection of ¹⁸F-FSU880 (101.8 - 346.5 MBq). The images were reviewed on a workstation (Advantage Workstation 4.6; GE Healthcare) by at least two board-certified nuclear medicine physicians. Any abnormal uptake greater than the surrounding background and not associated with physiological uptake considered positive. SUVmax was calculated by drawing a volume of interest placed around the target lesions. PET positive lesions were classified as local recurrences, metastases in the lymph node, bone and other sites. Patients were classified into four groups depending on their PSA level: 0.2 to < 0.5, 0.5 to < 1.0, 1.0 to < 2.0 and ≥ 2.0 ng/ml. The detection rate of recurrence sites was correlated with PSA level and Gleason score (GS) of the primary tumor. Mann-Whitney U test was used to evaluate difference in PSA values between groups with and without pathological uptake and between patients received RP and RT. SUVmax in 1h and 3h were compared using Wilcoxon test.

Results: Thirty-three patients (72 %) showed positive PSMA PET results, with a total of 62 lesions: 15 lesions in the prostate bed, 34 lesions in lymph nodes, 11 lesions in the bone and 2 lesions in the lung. The detection rates were 20% (1/5), 43% (3/7), 75% (6/8) and 88% (23/26), for PSA levels of 0.2 to < 0.5, 0.5 to < 1.0, 1.0 to < 2.0 and ≥ 2.0 ng/ml, respectively and 0 % (0/1), 56 % (10/18), 82 % (9/11) and 88 % (14/16) for GS 6, 7, 8 and 9, respectively. The PSA value was significantly higher in patients with positive PET results than those with negative results (4.3 ± 5.5 vs. 1.9 ± 3.4, p = 0.002) and significantly higher in patients post-RT than those post-RP (4.8 ± 6.3 vs 2.3 ± 2.9, p = 0.01). The detection rate in patients post-RP was 59 % (13/22) and that in patients post-RT was 83 % (20/24). SUVmax was significantly higher on PET images at 3h than at 1h (7.3 ± 5.9 vs 12.4 ± 10.5, p < 0.001). Of 62 lesions, 8 lesions (2 local recurrences and 6 lymph nodes) in 5 patients were depicted only at 3h.

Conclusions: Our preliminary data suggest that ¹⁸F-FSU880 would be a new PSMA-targeting promising tracer for detecting recurrence in patients with biochemical recurrence of prostate cancer