Bone Scan Index is an Independent Predictor for Time to Castration-Resistant Prostate Cancer in Newly Diagnosed Prostate Cancer: a Prospective Study

OBJECTIVE: To prospectively determine the prognostic value of the bone scan index (BSI) for time to development of castration-resistant prostate cancer (CRPC) in consecutive, hormone-naïve patients with newly diagnosed prostate cancer.

PATIENTS AND METHODS: Eligible patients participated in a prospective, observational, multi-center study of the value of bone scintigraphy (BS) at staging. BSI was determined using the EXINIBone(BSI)-software in 208 consecutive patients undergoing androgen deprivation therapy. The presence or absence of bone metastases at staging was classified by BS with or without supplementary imaging. Follow-up was performed >5 years after including the last patient.

RESULTS: During follow-up, 149 of the 208 patients (72%) were diagnosed with CRPC. Median time to CRPC was 20 months. Median follow-up time was 4.4 years in patients without CRPC. In univariate analyses, M1 (hazard ratio [HR] 3.00, 95% confidence interval [95%CI] 2.10 - 4.30), Gleason grade (HR 1.53, 95%CI 1.31 - 1.79), and BSI (HR 1.17, 95%CI 1.12 - 1.23) but not PSA significantly predicted time to CRPC (all, p<0.001). The predictive values of M1 (HR 2.06), Gleason grade (HR 1.47), and BSI (HR 1.10) were confirmed in multivariate analyses. Log-rank test for equality of time to CRPC showed the significant predictive value of BSI (BSI=0 vs. 0<BSI≤1 vs. BSI>1, p<0.001). In addition to routine assessment of M1 vs M0 status BSI contributed to the predictive power.

CONCLUSIONS: BSI is an independent risk factor for the time from ADT initiation to CRPC in hormone-naïve patients. The significant prognostic factors, in rank order, were M1-status, Gleason grade, and BSI.