Pre-test 68Ga-PSMA-ligand PET/CT positivity in early biochemical recurrent prostate cancer after radical prostatectomy—validation of a prediction model

Abstract

Objectives: The aim of this study was the validation of a recently established comprehensive and compact prediction model for 68 Ga-PSMA-11-ligand positron-emission tomography (PET) positivity with an independent subsequent patient series. Methods: A total of 292 consecutive patients with early biochemical recurrence after radical prostatectomy and PSA values between 0.2 and 1 ng/ml who underwent 68 Ga-PSMA-11-ligand PET/computed tomography (CT) between January 2016 and June 2017 were retrospectively included. The cohort was divided into a very low PSA value (0.2-0.5 ng/ml, n = 151) and a low PSA value (> 0.5-1 ng/ml, n = 141) subgroup. First, pre-test positivity probabilities for each patient were calculated according to the previously published comprehensive prediction model using all clinical variables (PSA value, ISUP grade group, T-and N-stage, patient under androgen deprivation therapy (ADT), previous radiation therapy) and the compact model using just the most predictive factors PSA value, ADT, and grade group. Then, all 68 Ga-PSMA-11-ligand PET/CTs were analysed by one experienced nuclear medicine physician, and the results were correlated to the calculated pre-test probabilities. Results: In the very low PSA value subgroup, mean pre-test probability for positive findings in 68 Ga-PSMA-11-ligand PET/CT was 57% (95% CI 55-60%) according to the compact model and 59% (95% CI 56-61%) according to the comprehensive model. In the low PSA value subgroup, mean pre-test probability was 72% (95% CI 70-74%) in the compact model and 74% (95% CI 72-76%) in the comprehensive model. After image analysis, 59% (89/151) of the patients in the very low PSA value subgroup revealed positive imaging findings. Seventy-nine percent (112/141) of the patients in the low PSA value subgroup presented with positive findings in the 68 Ga-PSMA-11-ligand PET/CT. The accuracy (AUC) of the prediction models was 0.71 (95% CI 0.65-0.78) for the compact model and 0.74 (95% CI 0.68-0.80) for the comprehensive model.

Survey by the French Medicine Agency (ANSM) of the imaging protocol, detection rate, and safety of 68Ga-PSMA-11 PET/CT in the biochemical recurrence of prostate cancer in case of negative or equivocal 18F-fluorocholine PET/CT: 1084 examinations

“…Several teams recently elaborated nomograms, which do not incorporate the results of FCH PET/CT, in contrast with ours. Rauscher et al [29] proposed two predictive models; a validation study [30] showed similar predictive values as ours, and the authors conclude that the prediction models should rather be understood as a tool for a positive decision towards a PSMA-ligand PET/CT examination. Another model integrating more clinical information has recently been proposed by Ceci et al [31] achieving a PPV of 81%, similar to ours, but a greater NPV of 76%.…”

Distribution of prostate cancer recurrences on gallium‐68 prostate‐specific membrane antigen (68Ga‐PSMA) positron‐emission/computed tomography after radical prostatectomy with pathological node‐positive extended lymph node dissection

“…Thus, currently 68 Ga‐PSMA PET/CT underestimates the extent of the disease, and patients with lymph node‐positive PCa often harbour microscopic metastatic PCa. Our detection rates, stratified by the different PSA values, are in accordance with earlier publications [12]. In our analysis, we did not focus on other predictors of positive 68 Ga‐PSMA PET/CT, such as grade group, and the study only included patients with high‐risk PCa, and the correlation between predictors and the chance of having a positive PSMA PET/CT has already been described and externally validated [12].…”

Multicenter External Validation of a Nomogram for Predicting Positive Prostate-specific Membrane Antigen/Positron Emission Tomography Scan in Patients with Prostate Cancer Recurrence

“…The same group proposed in-house validation of the model in an external cohort [26], showing high concordance of the calculated probabilities and PSMA-PET findings, while further external validation [27] did not confirm these results, showing an overestimation throughout the range of predicted positive PSMA-PET probabilities. However, this model cannot be fully compared with our nomogram, considering the strict patient selection and the lack of clinical data (eg, PSAdt and clinical setting).…”