ObjectiveTo demonstrate the effect of clinicopathological factors on Ga-68-PSMA-11 PET/CT positivity at the time of biochemical recurrence (BCR) of localized prostate cancer (PCa) following definitive therapy.MethodsWe retrospectively reviewed our institutional database for PCa patients who had BCR and subsequently underwent Ga-68-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 (pT1cT3b pN0-1 cM0) were included.Results37 out of 51 patients (72.5%) had positive Ga-68-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 >0.2ng/ml and PSA velocity of 1ng/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 0.71ng/ml for pre-scan PSA and 1.22ng/ml/yr for PSA velocity. In multivariable analysis, log pre-scan PSA and pre-scan PSA level>0.2ng/ml remained significant predictors for PSMA positivity, whereas the association of PSA velocity and of ADT was lost.ConclusionsIn BCR of localized PCa following definitive therapy, pre-scan PSA was strongly associated with positive Ga-68-PSMA-11 scan, even at PSA levels ranging from 0.2 to 1.0ng/ml. Therefore, clinical and pathological predictors of positive Ga-68-PSMA-11 PET/CT in PSA-only recurrence of localized prostate cancer need to be further elucidated.