5126 Background: Sunitinib is a multi-target tyrosine kinase inhibitor with anti-angiogenic and anti-proliferative activity mediated by signal blockade of VEGFR1/2, KIT, PDGFR α/β, and FLT-3. Sunitinib has recently been approved for the treatment of RCC. Several studies have identified biochemical thyroid function test (TFT) abnormalities in approximately 2/3 of pts under sunitinib treatment. The possible association of the incidence of sunitinib-induced thyroid dysfunction and progression-free (PFS) and overall survival (OS) has not been analyzed yet. Methods: Thyroid function was evaluated prospectively in pts with advanced RCC on days l and 28 of each treatment cycle. Sunitinib was given at a daily oral dose of 50 mg 4 weeks on, 2 weeks off. For the statistical analysis the Kaplan-Meier method was used to construct curves for PFS and OS. The log-rank test was used to compare between pts with and without biochemical thyroid abnormalities. The analysis has been performed with SAS (version 9.1). The alpha...