Bone Scan Index Is an Independent Predictor of Time to Castration-resistant Prostate Cancer in Newly Diagnosed Prostate Cancer: A Prospective Study

Abstract

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. Eligible patients participated in a prospective, observational, multicenter study of the value of bone scintigraphy (BS) at staging. BSI was determined using the EXINI BoneBSI 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. 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, presence of bone metastases (M1) (hazard ratio [HR] 3.00, 95% confidence interval [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 < .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 < .001). In addition to routine assessment of M1 vs M0 status, BSI contributed to the predictive power. BSI is an independent risk factor for the time from initiation of androgen deprivation therapy to CRPC in hormone-naïve patients. The significant prognostic factors, in rank order, were M1 status, Gleason grade, and BSI.