Background: We present results of an open label phase II study of the mTOR inhibitor Everolimus in patients (pts) with RAIR TC. Methods: Pts with metastatic, incurable RAIR TC who had shown radiographic progression within 6 months prior to enrollment received Everolimus 10mg orally once daily. Responses were monitored by CT's every two months. The primary endpoint was progression free survival. Sequential biopsies were obtained in selected pts. Results: Enrollment to the differentiated TC (DTC) cohort finished in Jan 2013 and included 33 pts, among them 11 with Hurthle cell TC. Exploratory cohorts enrolled 10 pts with medullary [MTC] and 5 with anaplastic [ATC] with 2 added openings remaining for ATC. For the DTC cohort, median time on study to date is 10 months (mo) (<1-23+). 31 pts are evaluable at this time. PFS in the DTC cohort by Kaplan-Meier (K-M) analysis is 16.0 mo (95%CI 10-NR). Currently, disease stability for 6 and 12 mo or more was achieved in 18 and 10/31 pts, respectively, 11 pts remain on study. Median OS was not reached but 1 year survival by K-M analysis was 76%. One pt achieved a PR. 3 pts with DTC underwent sequential biopsies which revealed activation of autophagy while markers for apoptosis were not detected. Among 10 MTC pts, one achieved a PR and 9 pts had stable disease for 6 mo or more (6-33+). Among 5 ATC pts, 3 progressed, one has ongoing disease stability for 5 mo. One patient achieved a complete response that lasted for 18 mo and whole exome sequencing revealed somatic loss of function mutation affecting the Tuberous Sclerosis 2 (TSC2) protein, a negative regulator of mTOR activity [TSC2 (Q1178*) and FLCN (R17fs)]. Most common treatment-related adverse events were as anticipated and included fatigue, stomatitis and infections. Grade (gr) 3 events included infection 5, weight loss 3, leukopenia 3, thrombocytopenia 3, fatigue 3, hypophosphatemia 2, stomatitis 2, pneumonitis 1 and thrombosis 1pts. One pt had gr 4 hypercholesterinemia and one pt had gr 4 leukopenia. Conclusions: Everolimus has significant anti-tumor activity in pts with advanced TC. Activation of autophagy could account for high rate of disease stability. Sequencing may identify mechanistic basis and predictive markers for treatment response. Clinical trial information: NCT00936858.