Background: Biomarkers of bone turnover, including urine N-telopeptide (uNTx) and serum C-telopeptide (sCTx) reflect tumor-related bone breakdown and have been used as surrogate measures of response to therapy in trials. Vascular endothelial growth factor (VEGF) levels correlate with extent of bone metastases (BM). We assessed whether vandetanib, an inhibitor of VEGF, epidermal growth factor receptor and RET signalling, improved uNTx response when added to fulvestrant (F) in patients with BM. Methods: Postmenopausal patients with bone only, or bone predominant, hormone receptor positive MBC were randomised to F (500mg IM day 1, 14, 28, then monthly) with either vandetanib (100mg PO OD) (FV) or placebo (FP) until progression. The primary objective was uNTx response (>30% reduction from baseline). uNTx was collected at baseline, weekly to wk 4, at wk 12 and then every 12 wks. Secondary objectives included PFS, OS, RECIST response, pain and toxicity. Results: 61 patients were allocated to FV and 68 to FP. Median age was 59. 18% had received 1 prior chemotherapy regime and 73% prior endocrine therapy for MBC. uNTx response (n=124 pts) was 64% for FV vs. 52% for FP (p=0.20). No difference was detected between groups for median PFS; 6 months for FV vs. 4.8 months for FP, HR=0.93 (95% CI: 0.64 to 1.36). 16 patients died in FV arm vs. 21 in the FP arm, HR=0.71 (95% CI: 0.37 to 1.36). For those patients with measurable disease, clinical benefit rates were 41% and 43%, respectively, p=1.00. Serious adverse events were similar, 3.3% for FV vs. 5.9% for FP. Elevated baseline uNTx (>65 nM BCE/mmol Cr) was prognostic for PFS, HR=1.62 (95% CI: 1.08 to 2.43 and for mortality, HR= 2.4 (95% CI: 1.2 to 4.6). In an exploratory analysis uNTx was predictive of responsiveness to FV for PFS, HR=0.60 when uNTx >65 vs. HR=1.37 when uNTx <65, P = 0.025 for interaction. Conclusions: The addition of vandetanib to F did not improve biomarker response, PFS or OS compared to F alone in patients with bone predominant disease. Exploratory analyses confirmed that baseline bone turnover markers are prognostic for PFS and OS. Clinical trial information: NCT00811369.