Tumour Volume Independently Predicts Metastasis in ISUP 2 Prostate Cancer

Background and Objectives: The outcomes for patients with localised prostate cancer are variable, even within defined tumour grades or clinical risk groups. Identifying features associated with disease aggression is imperative in contemporary PCa research. ISUP 2 PCa is particularly important in this regard as it exhibits a wide range of oncologic behaviour. The aim of this study was to evaluate the relationship between the tumour volume at radical prostatectomy (RP) and metastasis-free survival (MFS) in patients with ISUP 2 PCa. Methods: In this longitudinal multicentre cohort study, we reviewed the data of 809 consecutive patients with ISUP 2 PCa who underwent RP between 1996 and 2021. The tumour volume was estimated by summing the visual percentage involvement and multiplying it by specimen weight. Kaplan-Meier and Cox regression models were used to assess MFS. Linear regression was used to identify the preoperative predictors of the tumour volume (TV), with the appropriate assumption checks. Key Findings: The median TV was 2.9 cc (IQR: 1.4-7.0 cc). The TV categories were <2 cc (37%), 2-20 cc (53%), and >20 cc (11%). The median PSA follow-up was 42 months; 11% experienced biochemical recurrence (BCR). The BCR rates differed significantly across volume categories (p < 0.01). At 120 months, MFS was highest in the <2 cc group (97%) and lowest in the >20 cc group (87%) (p < 0.01). Conclusions and Clinical Implications: Prostate-TV in ISUP-grade group 2 disease is independently associated with MFS. Tumours > 20 cc warrant closer monitoring and may benefit from adjuvant therapy. The improved pre-operative prediction of TV could support more tailored treatment strategies, including suitability for surveillance. What does the study add? We demonstrate for first time that tumour volume at prostatectomy is correlated with metastasis-free survival in ISUP 2 PCa. At 120 months, MFS was highest in the <2 cc group (97%) and lowest in the >20 cc group (87%) (p < 0.01). This has implications for post-operative surveillance.