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Objectives: Assess the level of agreement between digital rectal examination findings of two urologists and its effect on risk prediction using the digital rectal examination based Rotterdam Prostate Cancer Risk Calculator.
Methods: Prospective cohort of asymptomatic unscreened men with PSA <=50.0 ng/mL and transrectal ultrasound volume <=110 mL who underwent transrectal ultrasound-guided prostate biopsy. Both urologists’ digital rectal examination findings were graded normal or abnormal (nodularity and/or induration), and volume classified as 25mL, 40mL or 60mL, according to the risk calculator algorithm. Inter-rater agreement analysis using Cohens’s kappa (κ) statistic was performed to determine consistency of digital rectal examination outcome and volume assessment. Receiver operating characteristic curve analysis and calibration plots were constructed to determine the effect of inter-rater differences. Decision curve analysis was applied to evaluate the clinical usefulness of the model.
Results: Of the 241 men included in the study, 41% (n = 98) had prostate cancer (81 were clinically significant). There was substantial agreement in the digital rectal examination (abnormal/normal) (κ = 0.78; P < 0.001) and volume estimation (κ = 0.79; P < 0.001). Receiver operating characteristic analyses showed good discrimination (0.75–0.78) and were comparable for both urologists. In our high risk cohort, at a probability threshold of 25%, the risk calculator reduces the prostate biopsy rate by 9%, without missing cancers.
Conclusions: Slight differences in digital rectal examination findings had very little impact on performance. The digital rectal examination based Rotterdam Prostate Cancer Risk Calculator can be considered a useful prostate biopsy outcome prediction tool.
