Predictive accuracy and clinical benefit of a nomogram aimed to predict 68Ga-PSMA PET/CT positivity in patients with prostate cancer recurrence and PSA < 1 ng/ml external validation on a single institution database

PURPOSE: To perform an external validation of a recently published nomogram aimed to predict positive 68Ga-PSMA-11 PET/CT in patients with biochemical recurrence (BCR) after radical prostatectomy (RP) by Rauscher et al. (Eur Urol 73(5):656-661, 2018). METHODS: Overall, 413 PCa patients with BCR after RP (two consecutive PSA ≥ 0.2 ng/ml) and PSA value between 0.2 and 1 ng/ml were included. A multivariable logistic regression model was produced to assess the predictors of positive 68Ga-PSMA-11 PET/CT results. The performance characteristics of the model were assessed by quantifying the predictive accuracy, according to model calibration. Yuden&#39;s index was used to find the best nomogram&#39;s cut-off. Finally, decision curve analysis (DCA) was implemented to quantify the nomogram&#39;s clinical value. RESULTS: In the external cohort, the overall detection rate of 68Ga-PSMA-11 PET/CT was 44% vs. 64.7% in the original population. At multivariate analysis, PSA at 68Ga-PSMA-11 PET/CT (OR: 7.06, p 35%. CONCLUSION: We assessed similar suboptimal predictive accuracies in the external cohort compared to the original one. PSA and ongoing ADT were confirmed as positive predictors, and the most informative nomogram cut-off resulted 35%.