External validation of a nomogram predicting the probability of prostate cancer Gleason sum upgrading between biopsy and radical prostatectomy pathology among Japanese patients

Abstract

Objectives: To explore the rate of upgrading in a contemporary cohort from 2 Japanese institutions, and evaluating the predictive accuracy of the nomogram when applied to patients, regardless of race. Previous reports have indicated that a maximum of 43% of men with prostate cancer will show an upgraded Gleason score from biopsy to radical prostatectomy (RP). A preparative nomogram was developed at the University of Hamburg to predict the probability of upgrading from biopsy to RP specimen.

Methods: Clinical and pathologic data of 503 patients from 2 Japanese institutions were supplied for validation. Nomogram-predicted probabilities of upgrading from biopsy to RP specimen were compared with actual rate of upgrading. The area under the receiver operating characteristic curve (AUC) was calculated for all patients. Calibration of the nomogram was achieved by comparing the predicted upgrading rate with that of an ideal nomogram.

Results: Gleason sum upgrading was recorded in 29.8% of patients at RP. Accuracy of the nomogram was 79.2% (confidence interval, 75.1%-83.2%). Overall AUC was 0.79 when applied to the validation dataset, with individual institutional AUCs ranging from 0.79-0.80. Nomogram predictions of upgrading were not within 10% of an ideal nomogram.

Conclusions: Gleason sum upgrading between biopsy and final pathology represents an important consideration in treatment decision-making, and nearly one third of patients with prostate cancer will be upgraded. The Hamburg nomogram seems to provide reasonably accurate predictions regardless of minor variations in pathologic assessment, but is not necessarily so accurate when applied to Japanese patient population.