Association between clinical response and toxicities with drug exposure in an alternative dosing regimen of sunitinib.

439 Background: An alternative dosing (AD) regimen of 37.5mg daily in repeated 4-weeks on, 2-weeks off cycle has been proposed to ameliorate frequent dose modifications due to toxicities as observed with the approved dosing regimen of sunitinib for metastatic renal cell carcinoma (mRCC). This study aims to determine the effect of drug exposure (sunitinib and active metabolite, SU12662) on clinical response and toxicities in patients receiving this AD regimen. Methods: All mRCC patients initiating AD sunitinib were invited to participate in this study. In week 4 of each cycle, toxicities were assessed and plasma steady-state levels (Cmax) were quantified using high-performance liquid chromatography. Clinical response was assessed after 2 treatment cycles; and was used with drug exposure and toxicities data for dose adjustments. Results: 36 patients with a mean age of 59.1 ± 10.1 years were recruited. Majority were males (81%) and Chinese (86%). Among the 24 and 16 analyzable cases for cycle 1 and 2, median...