Prospective Multicenter Validation of the Stockholm3 Test in a Central European Cohort

BACKGROUND: It has been shown that the Stockholm3 test decreases overdetection of prostate cancer (PCa) while retaining the ability to detect clinically significant PCa (csPCa) in a Swedish population. However, the test includes potentially population-specific testing of single-nucleotide polymorphisms and has yet not been validated outside Scandinavia. OBJECTIVE: To assess the performance of the Stockholm3 test in discriminating csPCa in a Central European cohort undergoing prostate biopsy (PBx). DESIGN, SETTING, AND PARTICIPANTS: This prospective multicenter validation study was conducted from August 2020 to September 2022 at two centers in Switzerland and one center in Germany. The study involved 342 men undiagnosed with PCa who were scheduled for PBx after prostate-specific antigen (PSA) testing and subsequent magnetic resonance imaging (MRI) of the prostate. Before PBx, participants had a blood sample taken for Stockholm3 testing. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary outcome was the accuracy of the Stockholm3 test in detecting csPCa (International Society of Urological Pathology grade group [GG] ≥2) according to the area under the receiver operating characteristic curve (AUC), sensitivity, and specificity, and the clinical consequences of using the model. RESULTS AND LIMITATIONS: The Stockholm3 test with a cutoff of 11% for csPCa detection had sensitivity of 92.3% (95% confidence interval [CI] 86.9-95.9%), specificity of 32.6% (95% CI 26.0-39.8%), a positive predictive value of 53.2% (95% CI 47.0-59.2%), and a negative predictive value of 83.6% (95% CI 73-91.2%). It showed superior discrimination for csPCa (AUC 0.77, 95% CI 0.72-0.82) in comparison to PSA (AUC 0.66, 95% CI 0.61-0.72; p < 0.001). Using a Stockholm3 cutoff of 11%, PBx could have been omitted for 73 men (21.0%), and 12/154 (8%) csPCa and 2/72 (2.8%) GG >2 cases would have been missed. Limitations include population selection bias. CONCLUSIONS: Our results show favorable clinical outcomes for the blood-based Stockholm3 biomarker test in a Central European patient cohort. PATIENT SUMMARY: The Stockholm3 blood test shows better accuracy in predicting prostate cancer than the more common PSA (prostate-specific antigen) test.