Background:mTOR upregulation has been reported to be involved in the pathogenesis of thyroid tumors and treatment with the mTOR inhibitor everolimus has shown promising results in endocrine tumors. We conducted a prospective phase II clinical trial to determine the efficacy and safety of everolimus in patients with advanced differentiated thyroid cancer.Patients and methods:Twenty-eight patients with progressive metastatic or locally advanced radioactive refractory differentiated thyroid cancer and 7 patients with anaplastic thyroid cancer were included and received everolimus 10mg orally once daily. The primary endpoint was disease control rate (complete (CR) + partial response (PR) + stable disease (SD) >24 weeks). Secondary endpoints included progression free survival (PFS), overall survival (OS), toxicity, mutational related outcomes and pharmacokinetic related outcomes (PK).Results:Median follow-up duration was 38 months (2-64). Seventeen patients (65%) showed SD, of which 15 (58%) showed SD > 24 weeks. No CR or PR were observed. Median PFS and OS were 9 (95%CI:4-14) and 18 (95%CI:7-29) months, respectively. Survival was negatively influenced by the presence of bone metastases. Toxicity was predominantly grade 1/2 and included anemia (64%), cough (64%), stomatitis (61%) and hyperglycemia (61%). Duration of SD was related to everolimus exposure. The presence of somatic gene variants related to mTOR signaling did not clearly stratify for responses.Conclusion:Everolimus has clinically relevant antitumor activity in patients with advanced differentiated thyroid cancer. Given the observed disease control rate and the relatively low toxicity profile, further investigation of everolimus in sequential or combination therapy in these patients is warranted.