Pathological Tumour Volume Percentage as a Quantitative Biomarker of Biological Aggressiveness in High-Risk Prostate Cancer

Background: Tumour volume percentage (TVP) is considered an important pathological parameter, particularly in prostate cancer, representing the ratio of tumour volume to the total gland, and it can be used to measure the quantity of malignancy. Previous reports have already demonstrated that an elevated tumour volume percentage is associated with unfavourable factors, including extraprostatic extension, positive surgical margins, and lymph node metastasis. The independent value of TVP, especially in high-risk prostate cancer treated by radical prostatectomy, remains an area of active research, despite established prognostic factors such as PSA, ISUP grade, and TNM stage. Materials and Methods: We retrospectively analyzed the records of 159 high-risk prostate cancer patients who underwent open or laparoscopic radical prostatectomy between January 2016 and January 2025 at the Clinic of Urology of Targu Mures. High-risk patients were defined as those with ISUP grade 4–5 or PSA >20 ng/mL or clinical stage ≥T2c or stage cT3–4 and/or lymph node metastasis. Tumour volume percentage was calculated from the final pathology result and was determined as the proportion of prostate cancer volume relative to the total prostate volume. Clinical and pathological features, including PSA, ISUP grade, TNM stage, surgical margin, and lymph node involvement, were reported. To assess TVP as an indicator of tumour aggressiveness, univariate and multivariate regression analyses were performed. A p-value < 0.05 was considered statistically significant. Results: A total of 159 high-risk prostate cancer patients (100%), with a median age of 66 years, who underwent open or laparoscopic radical prostatectomy were included. The median tumour volume percentage was 7.6%, and the median prostate volume was 43.8 cc. On univariate analysis, patients with extraprostatic extension (p < 0.001), positive surgical margins (p = 0.005), a higher ISUP grade (p < 0.001), and lymph node metastasis (p = 0.006) exhibited higher TVP compared to their counterparts. A significant correlation was also observed between TVP and the number of positive biopsy cores (p < 0.001), a higher PSA value (p = 0.005), and a younger age (p = 0.041). Conversely, no correlation was identified between TVP and perioperative factors such as hospital stay, surgery duration, ICU days, type of approach, or positive urine culture. Two regression models on multivariate analyses were performed with TVP as the dependent variable. In the continuous variable model (Adjusted R2 = 0.43, p < 0.001), independent predictors of higher TVP were the number of positive biopsy cores (B = 0.54, p < 0.001), the number of positive lymph nodes (B = 2.59, p < 0.001), and surgical margin dimension (B = 1.19, p < 0.001). Age, PSA, and perioperative variables showed no significant correlation with TVP on multivariate analysis. In the categorical regression model (Adjusted R2 = 0.438), statistical significance was confirmed (F-test, p < 0.001). Independent predictors of increased tumour volume percentage included ISUP grade 5 in the effect-coded model (B = +6.60, 95% CI: 0.96–12.25, p = 0.022), and pathological TNM stage pT4 (B = +24.70, 95% CI: 17.69–31.70, p < 0.001). ROC analysis showed limited-to-moderate discrimination for positive surgical margins (AUC = 0.655; 95% CI 0.565–0.744; p = 0.001) and stronger discrimination for pN1 (AUC = 0.793; 95% CI 0.650–0.936; p = 0.002). The Youden-derived cut-offs were 4.90% for positive surgical margins and 5.77% for lymph-node metastasis. Conclusions: Tumour volume percentage is significantly associated with several adverse pathological features in high-risk prostate cancer. Rather than a standalone biomarker, its association with adverse pathological features underscores its potential role in risk stratification models, and the incorporation into pathology reports and prognostic nomograms may improve clinical decision-making.