Analysis of different tumor volume thresholds of insignificant prostate cancer and their implications for active surveillance patient selection and monitoring

PURPOSE: We compared oncological outcomes according to tumor volume (TV) thresholds defining both classical and updated insignificant prostate cancer (IPC), since the TV threshold can be used as clinical parameter for active surveillance. METHODS: Between 2001 and 2012, we retrospectively analyzed 331 organ-confined prostate cancer patients who had preoperative Gleason score 6, preoperative PSA under 10 ng/mL and pathologic TV less than 1.3 mL. Among them, 81 of 331 (24.5%) had Gleason grade 4/5 disease postoperatively. Patients were stratified into two groups: (1) TV less than 0.5 mL, using the classical definition; and (2) TV between 0.5 mL and 1.3 mL, using the range of updated definition. We compared biochemical recurrence (BCR)-free survival and identified independent predictors of BCR in each group. RESULTS: Group 2 had more Gleason grade 4/5 disease than group 1 (P<0.001). On multivariate analysis, Gleason grade 4/5 disease was not associated with BCR in group 1 (P=0.132). However, it was an independent predictor for BCR in group 2 (P=0.042). BCR-free survival were not significantly different according to the presence of Gleason grade 4/5 disease in group 1 (P=0.115). However, in group 2, it was significantly different according to the presence of Gleason grade 4/5 disease (P=0.041). CONCLUSIONS: Although the TV thresholds of the two definitions of IPC vary only slightly, this difference was enough to result in different clinical course if Gleason grade 4/5 disease was present. Therefore, the updated IPC TV threshold should be carefully applied as clinical parameter for active surveillance.