Discordance between PSA level and bone metastatic volume is associated with unfavourable prognosis.

[OBJECTIVES] To evaluate the use of bone scan index (BSI)/initial prostate-specific antigen (iPSA) ratio, a novel biomarker that can reveal discordance between PSA level and bone metastasis volume, and to investigate its prognostic significance in patients with hormone-sensitive prostate cancer (PCa) and bone metastasis.

[PATIENTS AND METHODS] Clinical data were collected from 526 patients with bone metastatic PCa between 2009 and 2025 from multiple centres. Cancer-specific survival and overall survival (OS) were evaluated as clinical outcomes, and prognostic factors were analysed using multivariate Cox proportional hazard modelling and Kaplan-Meier methods. Survival tree analysis was performed to identify the optimal cut-off for stratifying prognosis. Propensity-score matching (PSM) was used to equalise patient baseline characteristics.

[RESULTS] The median age at diagnosis, initial PSA level and BSI were 75 years, 229.8 ng/mL and 1.6%, respectively. Survival tree analysis identified 0.02 as the optimal cut-off for BSI/iPSA ratio. Kaplan-Meier analysis showed that a high BSI/iPSA ratio (≥0.02) was associated with shorter OS compared with a low BSI/iPSA ratio (<0.02; hazard ratio [HR] 1.91; P < 0.0001). Statistical significance remained after PSM analysis (HR 1.63; P = 0.0303). Multivariate analysis showed that a high BSI/iPSA ratio was an independent prognostic factor for OS (HR 2.03; P = 0.0046). Notably, patients with a high BSI/iPSA ratio were less likely to have a PSA progression-only pattern of recurrence (P = 0.0122).

[CONCLUSIONS] Discordance between PSA level and bone metastatic volume indicated the presence of non-PSA-producing tumour and was correlated with increased risk of death. Our findings will help facilitate a personalised therapeutic approach for patients with metastatic prostate cancer.