Objective: To investigate the role of ⁶⁸Ga-PSMA PET/CT in predicting prostate specific antigen (PSA) response among castration-resistant metastatic prostate cancer patients receiving Abiraterone/ Enzalutamide treatment, based on the quantitative PET parameters such as SUVmax, SUVmean, highest SUVpeak, PSMA-TV and TL-PSMA, the biochemical parameters such as alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and the pathological parameters such as Gleason score.

Materials and Methods: A total of 45 patients initiating Abiraterone/Enzalutamide treatment after PSMA PET/CT in our clinic between January 2018 and January 2021 were included in this retrospective study. Data on whole body TL-PSMA, PSMA-TV, Highest SUVpeak (HPeak), Highest Background normalized SUVpeak (HBNSUVPeak), HSUVmax, HSUVmean, HBNSUVmax and HBNSUVmean values obtained by pre-treatment PSMA PET/CT imaging and pre- and post-treatment PSA values were recorded in each patient.

Results: ROC analysis revealed the cut-off values for predicting the progression to be ≥112.53 cm³ for PSMA-TV (AUC: 0.930±0.37 p<0.001), ≥857.1 for TL-PSMA (AUC:0.916±0.44 p<0.001) and ≥16.36 g/ml for Hpeak (AUC: 0.721±071 p=0.075), and the area under the curve had statistically significant high sensitivity and specificity in prediction of the progression. While both PSMA-TV (≥112.53 cm³) and TL-PSMA (≥857.1) values were associated with increased risk of progression in the univariate logistic regression analysis (OR and p values were OR: 29.7, p<0.001 and OR: 116, p<0.001, respectively), only the TL-PSMA value (≥857.1) was determined to be an independent prognostic factor in predicting progression (OR: 55.88, p:0.005) in the multivariate logistic regression analysis.

Conclusion: The TL-PSMA, as a parameter of ⁶⁸Ga-PSMA PET/CT and an independent prognostic factor in predicting the progression of the disease may contribute to the pre-treatment identification of patients who would not benefit from Abiraterone/Enzalutamide treatment and thus to provide timely guidance on use of alternative treatments.