Clinicopathological predictors of positive Ga-PSMA-11 PET/CT in PSA-only recurrence of localized prostate cancer following definitive therapy.

Objective: To demonstrate the effect of clinicopathological factors on Ga-PSMA-11 PET/CT positivity at the time of biochemical recurrence (BCR) of localized prostate cancer (PCa) following definitive therapy.

Methods: We retrospectively reviewed our institutional database for PCa patients who had BCR and subsequently underwent Ga-PSMA-11 PET/CT between April 2014 and February 2018. A total of 51 patients who were metastasis-free before PSMA imaging and previously treated with definitive therapy (radical prostatectomy or external beam radiotherapy) for localized disease (pT1c-T3b pN0-1 cM0) were included.

Results: 37 out of 51 patients (72.5%) had positive Ga-PSMA-11 PET/CT scans. Age at diagnosis, Gleason score (GS), D'Amico risk status of PCa, initial PSA level before treatment and PSA doubling time were not associated with PSMA positivity. Pre-scan PSA levels of > 0.2 ng/ml and PSA velocity of ≥ 1 ng/ml/year were significantly associated with increased PSMA positivity, whereas history of androgen deprivation therapy showed a trend towards significance. The optimal cutoffs for distinguishing between positive and negative scans were ≥ 0.71 ng/ml for pre-scan PSA and ≥ 1.22 ng/ml/yr for PSA velocity. In multivariable analysis, log pre-scan PSA and pre-scan PSA level > 0.2 ng/ml remained significant predictors for PSMA positivity, whereas the association of PSA velocity and of ADT was lost.

Conclusions: In BCR of localized PCa following definitive therapy, pre-scan PSA was strongly associated with positive Ga-PSMA-11 scan, even at PSA levels ranging from 0.2 to 1.0 ng/ml. Therefore, clinical and pathological predictors of positive Ga-PSMA-11 PET/CT in PSA-only recurrence of localized prostate cancer need to be further elucidated.