Positivity Rate of [F]Fluciclovine PET/CT in Patients with Suspected Prostate Cancer Recurrence at PSA Levels Below 1 ng/mL.

Purpose: Early and precise localization of recurrent prostate cancer lesions after local therapy facilitates optimal disease management. Here, we present results from a single-center study to evaluate the utility of [F]fluciclovine PET/CT to localize prostate cancer recurrence in patients with PSA <1 ng/mL.

Procedures: Data from men who underwent [F]fluciclovine PET/CT (August 2016-March 2020) for suspected recurrent prostate cancer and who had a PSA value <1ng/mL were retrospectively reviewed. The number of positive scans (positivity rates, PR) was calculated for the whole body, prostate/bed, and extraprostatic regions (pelvic or extrapelvic lymph nodes, bones, and soft tissue). PR were stratified by pre-scan PSA.

Results: Data from 113 patients were included. In total, 98 (87%) were post-prostatectomy and 15 (13%) had received non-surgical primary therapy. Twenty patients (18%) were receiving ADT at the time of the scan, 91 (81%) were not, and ADT status was not known for 2 (1.8%) patients. The overall PR at PSA <1ng/mL was 59% (67/113). For the prostate/bed, it was 35% (40/113), and for extraprostatic locations, it was 37% (42/113). At PSA >0-<0.2, 0.2-<0.5, and 0.5-<1 ng/mL, the overall PR was 43% (10/23), 70% (35/50), and 55% (22/40), respectively. In the prostate/bed, these were 13% (3/23), 50% (25/50), and 30% (12/40), respectively, and in extraprostatic lesions were 30% (7/23), 44% (22/50), and 33% (13/40), respectively. Pelvic lymph nodes were the most common site for extraprostatic lesions (29/113, 26%). PR in extrapelvic lymph nodes, bone, and soft tissue were 8.0%, 12%, and 3.5%, respectively. Soft tissue lesions comprised lung nodules (n=3) and a perirectal mass implant (n=1).

Conclusions: Despite low PSA values, more than half of patients had positive [F]fluciclovine PET/CT findings. Patients with low PSA levels may demonstrate suspicious findings outside of the pelvis, including abdominal lymph nodes and metastatic disease to bones and lungs.