Background: Tivozanib hydrochloride (tivozanib) is a potent, selective, tyrosine kinase inhibitor of all three vascular endothelial growth factor receptors, with a long half-life and has shown superior efficacy, measured as progression-free survival (PFS), as first-line, targeted therapy vs. sorafenib in a phase III trial (TIVO-1) in patients with advanced renal cell carcinoma (J Clin Oncol2012;30[suppl]:Abstract 4501). Patients who progressed (PD) on sorafenib could receive tivozanib in an open-label, prospective multicenter extension study of TIVO-1. We report preliminary efficacy and safety data for patients who had PD on sorafenib and subsequently received tivozanib in this extension study. Methods: Patients with PD on sorafenib, per RECIST version 1.0, were eligible to receive tivozanib dosed at 1.5 mg/day PO for 3 weeks followed by a 1-week rest, in repeated 4-week cycles, until PD or unacceptable toxicity. Patients were to have been no more than 4 weeks from last dose of sorafenib until initiation of tivozanib, and have an ECOG performance status of ≤2. Dose adjustments were performed as previously reported. Objectives included assessing objective response rate (ORR), duration of response, PFS for tivozanib following PD on sorafenib, and overall survival. Results: As of January 20, 2012, 127 patients (72.4% male) were evaluable for response. Median age was 59.0 years (range: 23–85 years). ORR was 7.9% (95% CI 3.8–14.0%; partial response [PR]=7.9%; stable disease [SD]=65.4%; PD=18.9%), and 71.3% of patients showed tumor shrinkage. Median duration of PR was 11.1 months (95% CI ≥7.5 months). Median duration of SD was 12.7 months (95% CI ≥7.4 months). Median PFS was 5.6 months (95% CI 5.4–9.1 months). Median OS was not yet reached. Most commonly reported treatment-emergent adverse events (all grades/Grade ≥3) were hypertension (22.4%/10.2%), asthenia (11.0%/3.1%), fatigue (11.0%/3.9%), palmar-plantar erythrodysesthesia (11.0%/1.6%), and diarrhea (10.2%/1.6%). Conclusions: Tivozanib has anti-tumor activity after PD on sorafenib. The adverse-event profile of tivozanib after sorafenib is similar to that observed in TIVO-1. Clinical trial information: NCT01076010.