PREDICTION OF INDOLENT PROSTATE CANCER: VALIDATION AND UPDATING OF A PROGNOSTIC NOMOGRAM TO SUPPORT DECISION-MAKING ON SURGERY
Ewout W. Steyerberg, PhD1, Monique Roobol, PhD2, Michael Kattan3, and Fritz Schröder, PhD2. (1) Department of Public Health, AE 236, Rotterdam, Netherlands, (2) Dept of Urology, Rotterdam, Netherlands, (3) Cleveland Clinic Foundation, Cleveland, OH
Purpose: Screening with serum prostate specific antigen (PSA) testing leads to the detection of many prostate cancers early in their natural history. Statistical models may predict the presence of ‘indolent cancer', which do not require surgical resection. We aimed to validate and update model predictions for a screening setting. Patients and Methods: We selected 247 clinical stage T1C or T2A patients from the European Randomized Study on Screening for Prostate Cancer who were treated with radical prostatectomy. We validated a nomogram, which was previously developed in a clinical setting. Predictive characteristics included serum PSA, ultrasound prostate volume, clinical stage, prostate biopsy Gleason grades 1 and 2, and length of cancer and non-cancer tissue in biopsy cores. Indolent cancer was defined as organ confined cancer <=.5cc in volume and without poorly differentiated elements. Logistic regression was used to update the previous model and to examine the contribution of other potential predictors. Results: Overall 121 (49%) of 247 patients had indolent cancer, while the average predicted probability was 20% (p<0.001). Effects of individual variables were similar to those found before, and discriminative ability was adequate (area under the receiver operating characteristic curve 0.76). An updated model was constructed which merely recalibrated the nomogram, and did not apply additional predictors. Conclusions: Prostate cancers identified in a screening setting have a substantially higher likelihood of being indolent than predicted by a previously proposed nomogram. An updated model can however support patients and clinicians in their decision-making on treatment options for prostate cancer.