Quantitative bone scan lesion area as an early surrogate outcome measure indicative of overall survival in metastatic castration-resistant prostate cancer.

Abstract

179 Background: Bone Scan Lesion Area (BSLA) is a biomarker that can be computed semi-automatically from whole-body scintigraphic imaging as a measure of overall bone tumor burden. Initial development and validation, including correlation with outcomes, was performed in trial cohorts from a single drug treatment with controls in subjects with metastatic castrate-resistant prostate cancer (CRPC). A 30% increase/decrease in BSLA was defined as progression/response on bone scan. We hypothesize that, when applied to an independent treatment trial cohort with a different mechanism of drug action, baseline BSLA and Week 12 change post-treatment are predictive of a subject's overall survival. Methods: From an anonymized imaging research database a cohort of 198 CRPC subjects was identified who enrolled in a treatment trial (127 treated, 71 placebo). This cohort was independent of those used for biomarker development and initial validation, and involved a different mechanism of drug action. Subjects underwent standard of care whole-body bone scintigraphy with 99mTc-Methyl diphosphonate (99mTc-MDP). BSLA was calculated at baseline and response at Week 12. Multivariate Cox regression was used to test whether (1) baseline BSLA, and (2) early changes in BSLA (12 weeks post treatment) were predictive of overall survival. Results: BSLA < 2000 mm2 at baseline was a prognostic factor (HR=0.6; p=0.003) and predictive of longer survival (HR=0.4; p<0.001). Subjects without PD by BSLA at Week 12 had significantly longer survival than subjects with PD: median 170 days vs. 186 days in the placebo group and 260 days vs. 392 days in the treatment group. The overall survival rates between non-PD and PD subjects were statistically different (HR=0.64, p=0.007). Conclusions: BSLA is calculated semi-automatically from bone scans and provides a quantitative and objective treatment response assessment. Baseline BSLA and early changes post treatment were found to be predictive of overall survival in patients with metastatic castration-resistant prostate cancer. BSLA has now been demonstrated to be an early surrogate outcome for overall survival in different drug treatments.