Prostate Cancer Index Density, the Ratio of Percentage of Biopsy-Positive Cores to Prostate Volume, and Predicted Lethal Disease in the EAU Intermediate Prognostic Risk Class: Analysis and Implications in 651 Consecutive Patients Treated with Robot-Assisted Radical Prostatectomy at a Tertiary Referral Centre

: Background/Objectives: The ratio of percentage of prostate cancer (PCa) biopsy-positive cores (BPC) to prostate volume as the index density factor (Id-BPC) was used to predict the risk of high tumour grades in the surgical specimens of European Association of Urology (EAU) intermediate-risk patients treated with robotic surgery. Methods: From January 2013 to December 2021, we evaluated 651 patients without any prior treatment for PCa. In the surgical specimen, tumour grades were classified as indolent (International Society of Urological Pathologists Classification (ISUP) 1), significant (ISUP 2/3), and lethal (ISUP 4/5). Associations with the risk of significant and lethal cancers were assessed by the multinomial logistic regression model. Results: Tumour grade was clinically significant (ISUP 2/3) in 522 (80.2%) cases and lethal (ISUP 4/5) in 99 (15.2%), while the results were not significant (ISUP 1) in 30 (4.6%) subjects. The association of Id-BPC was always stronger than BPC for ISUP 1 vs. 4/5 (OR = 0.284; 95% CI: 0.128-0.632; p = 0.002), ISUP 2/3 vs. 4/5 (OR = 0.744; 95% CI: 0.586-0.946; p = 0.016), and ISUP 1 vs. 2/3 (OR = 0.382; 95% CI: 0.176-0.828; p = 0.015), and this trend held after adjusting for clinical factors. Conclusions: Accordingly, Id-BPC was positively associated with lethal disease, as, when it increased or decreased, it was more or less likely, respectively, to find ISUP 4/5 in the surgical specimens of the operated subjects, who could have been stratified according to Id-BPC risk levels.