Prospective validation of a risk calculator which calculates the probability of a positive prostate biopsy in a contemporary clinical cohort

Abstract

BackgroundPrediction models need validation to assess their value outside the development setting. ObjectiveTo assess the external validity of the European Randomised study of Screening for Prostate Cancer (ERSPC) Risk Calculator (RC) in a contemporary clinical cohort. MethodsThe RC calculates the probability of a positive sextant prostate biopsy (P(posb)) using serum prostate-specific antigen (PSA), results of digital rectal examination, transrectal ultrasound (TRUS) and ultrasound assessed prostate volume. We prospectively validated the RC in 320 biopsied men (55–75years), with no previous prostate biopsy, included in five Dutch hospitals in 2008–2011. If the P(posb) was ⩾20% a biopsy was recommended.The performance of the RC was tested by comparing the observed outcomes to predicted probabilities, using the area under the curve (AUC) and decision curves analyses. ResultsCompared to the screening cohort, men in the clinical cohort differed. They had higher PSA levels (median 6.8 versus 4.3ng/ml, p<0.01), less TRUS-lesions (27% versus 34%, p=0.01) and more prostate cancer (PCa) at biopsy (43% versus 25%, p<0.01). Mainly eight biopsy cores were taken. Despite the differences between these cohorts, the mean observed probability agreed with the mean predicted probability (43% versus 40%). The RC predicted P(posb) better than a model with PSA and digital rectal examination, AUC 0.77 (95% confidence interval (CI) 0.72–0.83) and 0.71 (95%CI 0.65–0.76, p<0.01), respectively. This was confirmed by the decision curves analysis. Under the 20% threshold, 17% (11/63) of the biopsied men were diagnosed with PCa. Two of 11 men had an important cancer (Gleason 3+4). ConclusionsThe ERSPC RC performs well in a Dutch clinical cohort in men with previous PSA tests and contemporary biopsy schemes, and outperforms a PSA and DRE-based approach in the decision to perform a biopsy.