OBJECTIVE: To investigate the clinical implications of interobserver variation in the assessment of re-biopsies obtained during active surveillance (AS).

MATERIAL AND METHODS: A total of 107 low-risk prostate cancer patients with a total of 93 diagnostic biopsy sets and 109 re-biopsy sets were included. The ISUP 2005 Gleason scoring system was applied for the histopathological assessment of all biopsies. Three different definitions of histopathological progression were applied. Unweighted and linear weighted Kappa statistics were used to compare the interobserver agreement.

RESULTS: The overall GS agreement was 68.8% with a weighted Kappa of 0.670. The interobserver agreement was 79.6% with regard to meeting the AS selection criteria. According to the three progression definitions applied, overall agreement was between 80.7-89.0% with weighted Kappa values of 0.746-0.791. Treatment recommendations would have changed in up to 10.1% (95% CI: 5.4%-17.7%) of the 109 re-biopsy sets.

CONCLUSION: Kappa statistics demonstrated a strong agreement between the histological evaluations. Still, up to 10% of AS patients would receive different treatment recommendation depending upon which histopathological evaluation of re-biopsies was used for treatment planning.