VERIFY study is a randomized, double-blind, multicenter phase III clinical trial aimed to determine the efficacy and safety of vandetanib in tyrosine kinase inhibitor-naive patients with locally advanced or metastatic differentiated thyroid cancer (DTC), refractory to radioiodine (RAI) therapy with documented progression (NCT01876784). Patients were randomized 1:1 to vandetanib or placebo. The primary endpoint was progression-free survival (PFS). Secondary endpoints included best objective response rate, overall survival (OS), safety, and tolerability. Patients continued to receive randomized treatment until disease progression or for as long as they were receiving clinical benefit unless criteria for treatment discontinuation were met. Following randomization, 117 patients received vandetanib and 118 patients received placebo. Median PFS was 10.0 months in the vandetanib group and 5.7 months in the placebo group (hazard ratio [HR] 0.75; 95% confidence interval [CI] 0.55–1.03; p = 0.080). OS was not significantly different between treatment arms. Common Terminology Criteria for Adverse Events [CTCAE] adverse events of grade ≥3 were reported in 55.6% of patients in the vandetanib arm and 25.4% in the placebo arm. Thirty-three deaths (28.2%; one related to study treatment) occurred in the vandetanib arm compared with 16 deaths (13.6%; two related to treatment) in the placebo arm. No statistically significant improvement was observed in PFS in treatment versus placebo in patients with locally advanced or metastatic, RAI-refractory DTC. Moreover, active treatment was associated with more adverse events and more deaths than placebo though the difference in OS was not statistically significant.