Prostate Cancer Testing Between Screening Rounds: Evidence from the STHLM3-MRI Trial.

Background and objective: The STHLM3-MRI screening-by-invitation trial found that magnetic resonance imaging (MRI)-based screening for prostate cancer (PCa) improved early detection in comparison to systematic biopsy. The aim of the present study was to describe testing and PCa incidence between screening rounds of the STHLM3-MRI trial.

Methods: The study population comprised men aged 50-74 yr in the MRI (experimental) arm of the STHLM3-MRI trial without a PCa diagnosis in the first round. We defined three risk groups: low risk (baseline prostate-specific antigen [PSA] <1.5 ng/ml; not invited to the second round after 2-3 yr); non-elevated risk (1.5 ≤PSA <3 ng/ml and Stockholm3 score <11%); and elevated risk (PSA ≥3 ng/ml or Stockholm3 score ≥11%). Interval events included PSA tests, MRI examinations, biopsies, and PCa detection.

Key findings and limitations: In the study population of 7256 men, 33% had at least one PSA test, 2.2% had an MRI examination, 0.8% had a biopsy, 0.3% had a PCa diagnosis, and 0.2% (n = 17) had International Society of Urological Pathology grade group ≥2 PCa between screening rounds. Stratified by risk, 27%, 40%, and 54% of men with low risk (n = 5009), non-elevated risk (n = 1200), and elevated risk (n = 1047), respectively, had a PSA test. The PCa detection rate was low but increased with risk level, at 0.1% for low risk, 0.3% for non-elevated risk, and 1.4% for elevated risk. These results are specific to Sweden and depend on the interval length between screening rounds.

Conclusions and clinical implications: We observed a substantial testing rate of 33% between STHLM3-MRI screening rounds, but few PCa cases were detected among men with lower risk. Most cancers were diagnosed in the elevated-risk group. A reduction in opportunistic testing in lower-risk groups will be crucial for optimising the benefits of future screening programmes.