Stockholm3 Versus PSA in Prostate Cancer Screening: A Synthesis of 9-year Outcomes, Repeat Screening, and Multiethnic Validation

Highlights

• The Stockholm3 (S3) test demonstrates superior longitudinal predictive value over 9 years compared to PSA, identifying aggressive cancers even in men with low PSA levels (<3 ng/ml).
• In repeat screening settings, S3 (at a threshold of ≥0.15) can reduce the need for magnetic resonance imaging (MRI) by 41% without compromising the detection of high-risk (Gleason ≥4+3) cancers.
• The SEPTA trial confirms S3’s performance across diverse ethnic populations (Black, Asian, Hispanic), maintaining sensitivity while offering nearly three times the specificity of PSA.
• Clinical implementation of S3 facilitates a shift toward precision screening, significantly mitigating the public health burden of overdiagnosis and unnecessary biopsies.

Background

Prostate-specific antigen (PSA) has served as the cornerstone of prostate cancer (PCa) screening for decades. However, its clinical utility is hampered by a significant lack of specificity, leading to a high rate of false positives, overdiagnosis of indolent tumors, and unnecessary invasive biopsies. Conversely, PSA can be deceptively low in patients harboring aggressive, clinically significant prostate cancer (csPC). The standard threshold of 3 or 4 ng/ml often fails to provide a precise risk assessment.

Emerging as a solution, the Stockholm3 test is a multianalyte blood-based algorithm that integrates plasma protein biomarkers (PSA, free PSA, human kallikrein 2 [hK2], growth differentiation factor 15 [GDF15], and prostate secretory protein 94 [PSP94]), genetic markers (a polygenic risk score based on 232 single-nucleotide polymorphisms), and clinical data (age, family history, and prior biopsy results). Recent high-impact publications, including 9-year follow-up data from the STHLM3 trial, repeat screening analyses in the MRI era, and multiethnic validation via the SEPTA trial, provide a robust evidentiary basis for transitioning beyond PSA-only screening models.

Key Content

Long-term Clinical Significance: The 9-Year STHLM3 Outcomes

Long-term data are critical for validating screening tools in PCa due to the slow-growing nature of many tumors. Vigneswaran et al. (2026) analyzed 968 men from the original STHLM3 screening trial (total n=59,088) who were treated with radical prostatectomy or radiotherapy. This study is pivotal as it links baseline screening results to long-term oncological outcomes, specifically biochemical recurrence (BCR) and PCa-specific mortality.

Key findings revealed that men with elevated S3 (≥11) but low PSA (<3 ng/ml) had a substantially higher risk of aggressive disease. The 5-year cumulative rate of high-risk BCR for the “elevated S3 alone” group was 5.3%, significantly higher than the 0% seen in men with elevated PSA alone. When comparing the two groups, S3-only elevation carried a hazard ratio (HR) of 8.8 (95% CI 1.06–72; p=0.044) for high-risk BCR compared to PSA-only elevation. This suggests that the Stockholm3 test identifies aggressive phenotypes that PSA thresholds overlook, while also suggesting that a high PSA with a low S3 score indicates a lower risk of clinical recurrence, allowing for the safe deferral of biopsy.

Stockholm3 in Repeat Screening and the MRI Era

The integration of MRI into the diagnostic pathway has improved detection but increased the resource burden on healthcare systems. Discacciati et al. (2025) performed a secondary analysis of the STHLM3-MRI trial to evaluate S3 in repeat screening (2–3 years after the initial round). The study compared S3 performance to PSA in a cohort of 1,500 men.

For the detection of Gleason ≥7 cancer, S3 showed a significantly higher Area Under the Curve (AUC) of 0.765 compared to 0.651 for PSA. Utilizing a threshold of S3 ≥0.15 for MRI referral resulted in 41% fewer MRI scans (Relative Positive Fraction [RPF] 0.59) compared to using a PSA ≥3 ng/ml threshold. Crucially, this reduction in imaging did not miss high-grade (Gleason ≥4+3) cancers (RPF 1.00). These findings indicate that S3 acts as an effective filter in the repeat screening setting, optimizing the use of expensive MRI resources.

Validation Across Diverse Populations: The SEPTA Trial

A major criticism of many PCa screening tools is the lack of validation in non-White populations, who often face higher PCa mortality rates. The SEPTA trial (Vigneswaran et al., 2024) addressed this by recruiting 2,129 participants across 17 sites, including Black (24%), Asian (16%), and Hispanic (14%) men.

Stockholm3 demonstrated noninferior sensitivity to PSA ≥4 ng/ml (relative sensitivity 0.95) but nearly triple the specificity (relative specificity 2.91). This superior performance was consistent across all racial and ethnic subgroups. In this diverse cohort, the application of S3 could have avoided 45% of benign or low-grade (ISUP 1) biopsies. This multiethnic validation is a critical step for global guideline inclusion, ensuring that precision screening tools are both equitable and effective.

Expert Commentary

The collective evidence from these three major trials represents a paradigm shift. Historically, the medical community struggled with the “PSA paradox”: detecting too many indolent cancers (overdiagnosis) while missing aggressive ones. Stockholm3 addresses this by incorporating genetic and protein-level complexity that a single marker like PSA cannot provide.

From a biological perspective, the inclusion of KLK2 and GDF15 provides insight into tumor activity and inflammatory states that are often associated with high-grade disease. The polygenic risk score adds a baseline of genetic susceptibility that remains stable regardless of current prostatic volume or inflammation.

However, limitations remain. While the 9-year follow-up is impressive, PCa-specific mortality data are still maturing. Furthermore, the cost-effectiveness of Stockholm3 depends on the health system’s structure; in systems where MRI is cheap and accessible, the ‘filter’ value of S3 might be perceived differently than in systems with long wait times for imaging. Nevertheless, the SEPTA trial’s results are a powerful rebuttal to the idea that risk-predictive tests are only valid for European populations.

Conclusion

The Stockholm3 test has reached a level of evidentiary maturity that justifies its integration into clinical practice as a primary screening tool or as a secondary triaging mechanism. By identifying aggressive cancers at lower PSA thresholds and reducing unnecessary MRIs and biopsies by nearly 45%, S3 achieves the dual goal of improved cancer detection and reduced healthcare harm. Future research should focus on the cost-benefit analysis of broad population implementation and its long-term impact on mortality rates compared to MRI-only pathways.

References

• Vigneswaran HT, et al. Stockholm3 Versus Prostate-specific Antigen in Prostate Cancer Screening: 9-year Outcomes Demonstrating Improved Detection of Aggressive Cancers and Reduced Overdiagnosis from the STHLM3 Trial. Eur Urol. 2026;89(1):82-90. PMID: 41107178.
• Discacciati A, et al. Repeat Prostate Cancer Screening using Blood-based Risk Prediction or Prostate-specific Antigen in the Era of Magnetic Resonance Imaging-guided Biopsies: A Secondary Analysis of the STHLM3-MRI Randomized Clinical Trial. Eur Urol Oncol. 2025;8(6):1466-1473. PMID: 39562218.
• Vigneswaran HT, et al. Stockholm3 in a Multiethnic Cohort for Prostate Cancer Detection (SEPTA): A Prospective Multicentered Trial. J Clin Oncol. 2024;42(32):3806-3816. PMID: 39038251.