Objective To more clearly elucidate the association between prostate volume and Gleason score (GS) upgrading. Patient and Methods We reviewed 451 patients with prostate cancer with a GS of 6 on biopsy, who underwent radical prostatectomy without neoadjuvant treatment. As a preoperative variable, we assessed the independent effect of prostate volume on GS upgrading. To evaluate the association between prostate volume and GS upgrading, we developed multivariate models with volumetric pathological variables, including postoperative tumour volume and percent tumour volume (tumour volume as a percentage of prostate volume). Results GS upgrading was observed in 194 patients (43.0%). As a preoperative variable, smaller prostate volume was an independent predictor of GS upgrading. In regression analysis, prostate volume and postoperative tumour volume were inversely correlated. On multivariate analysis including volumetric pathological variables, tumour volume was a strong independent factor influencing GS upgrading, and prostate volume lost statistical significance after adjusting for tumour volume. Percent tumour volume was inversely correlated with GS upgrading after adjusting for tumour volume. Conclusions Smaller prostate volume was an independent predictor of GS upgrading as a preoperative variable. The inverse relationship between prostate volume and GS upgrading seems to be attributable to cancer biology, which was represented by tumour volume in our study. Percent tumour volume was also inversely associated with GS upgrading. These results suggest that biological factors and sampling error both play important roles in GS upgrading.
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