Introduction & objectives
To develop a clinical nomogram aimed to predict which patients with recurrent prostate cancer (PCa) could benefit from 68Gallium-Prostate Specific Membrane Antigen Positron Emission Tomography/Computed Tomography (68Ga-PSMA PET/CT).
Materials and methods
We retrospectively enrolled 703 PCa patients with confirmed biochemical recurrence (BCR) after radical prostatectomy (n=684) and primary radiotherapy (n=19). Each man underwent 68Ga-PSMA PET/CT to identify the site of recurrence. Patients were stratified according to different clinical settings of recurrence (First PSA relapse, BCR after salvage therapy, PSA persistence after primary therapy and disease progression before starting systemic therapies in 325, 241, 76 and 61 patients, respectively). First, we assessed the detection rate of 68Ga-PSMA PET/CT in overall population and in each subgroup of patients. Second, multivariate logistic regressions were used to determine which co-variates (including ISUP group, PSA at 68Ga-PSMA PET/CT, PSA doubling time, ongoing androgen deprivation therapy [ADT] at 68Ga-PSMA PET/CT, time to recurrence and the clinical setting) independently predict a positive 68Ga-PSMA PET/CT result. Finally, regression-based coefficients were used to develop a nomogram predicting positive 68Ga-PSMA PET/CT result and 200 bootstrap resamples were used for internal validation.
Results
Table 1 reports patients’ perioperative characteristic. Median PSA at 68Ga-PSMA PET/CT was 0.7 ng/ml (IQR 0.4- 1.3). Overall, 116 (16.5 %) men were on-going with ADT at the time of 68Ga-PSMA PET/CT. Median time to BCR was 21 months (IQR 9-49); median PSA doubling time was 6 months (IQR 4-10). The overall detection rate of 68Ga-PSMA PET/CT was 51.2 %.
Table 2 reports PET-CT diagnostic performance among the different subgroups: detection rate was 40.3 %, 54 %, 60.5% and 86.9 % in patients with first PSA relapse, BCR after salvage therapy, PSA persistence after primary therapy and disease progression before starting systemic therapies, respectively; p<0.001). At multivariable analysis ISUP grade group, PSA level at 68Ga-PSMA PET/CT, PSA doubling time and the clinical setting were found to be independent predictors of positive 68Ga-PSMA PET/CT results (all p≤0.04). A nomogram based on covariates included in the multivariate model demonstrated bootstrap-corrected predictive accuracy of 82%.
Conclusions
Our nomogram could help physician to select patients with different scenario of recurrence who may benefit from 68Ga-PSMA PET/CT restaging.
