RET and differentiated thyroid carcinoma: A phase III study of sorafenib in RAI-resistant differentiated thyroid cancer confirmed PFS of 10.8 months versus placebo, but tumor shrinkage was observed only in 10% of patients.42 Randomized, double-blind, phase II trial of vandetanib, a TKI of RET, VEGFR, and EGFR signaling, in patients with refractory to radioactive iodine therapy demonstrated significant PFS of 11.1 months compared with 5.9 months in the placebo group.