Abstract
578 Background: Sunitinib malate (SU11248) is a multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activity that specifically inhibits VEGFR, PDGFR, KIT, RET and FLT3. In a phase II trial of 64 patients with refractory, metastatic breast cancer, sunitinib treatment resulted in an ~11% objective response rate (Miller et al, ASCO 2005). To characterize potential biomarkers of biological response to sunitinib, we analyzed plasma levels of a panel of soluble proteins from patients in this trial. Methods: Patients received sunitinib in 6-week cycles comprised of 50 mg/day for 4 weeks followed by 2 weeks off treatment. Pre-dose plasma samples from 62 patients were obtained on days 1, 14, and 28 of the first cycle and days 1 and 28 of subsequent cycles. Plasma levels of VEGF, soluble VEGF receptor 2 (sVEGFR-2), soluble KIT (sKIT), and a novel biomarker, sVEGFR-3, were measured via ELISA analysis. Results: Plasma levels of each protein were modulated in most patients d
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