A randomized phase II efficacy and safety study of vandetanib (ZD6474) in combination with bicalutamide versus bicalutamide alone in patients with chemotherapy naïve castration-resistant prostate cancer.

PURPOSE: To investigate the efficacy and safety of combining vandetanib, an orally available multi-targeted tyrosine kinase inhibitor of vascular endothelial growth factor receptor-2 (VEGFR-2) and epidermal growth factor receptor (EGFR), with bicalutamide in patients with metastatic castration-resistant prostate cancer (mCRPC).

METHODS: This was an open-label, randomized phase II multi-center study. Eligible patients had rising PSA on androgen deprivation therapy, minimal symptoms and were chemotherapy-naïve. Protocol therapy was either vandetanib 300 mg oral daily plus bicalutamide 50 mg oral daily (Arm A) or bicalutamide 50 mg oral daily alone (Arm B) with cross-over to vandetanib monotherapy at progression. The primary endpoint was PSA response (≥ 50 % decline from baseline).

RESULTS: Thirty-nine patients were recruited, 19 in Arm A and 20 in Arm B. PSA response was comparable in Arm A and Arm B (18 vs. 19 %). Time to PSA progression was 3.16 months (95 % confidence interval (CI): 1.09, not reached (NR)) for Arm A and 3.09 months (95 % CI: 1.22, NR) for Arm B. Treatment discontinuation due to adverse events was more common in Arm A compared to Arm B (42 vs. 5 %; p = 0.019). Treatment with vandetanib was associated with a reduction in soluble VEGFR-2 levels after two cycles but an increase in plasma VEGF levels.

CONCLUSION: The combination of vandetanib and bicalutamide was associated with considerable toxicity and did not have superior efficacy over bicalutamide alone. Further evaluation of this combination is not warranted in mCRPC.