Sunitinib is an anticancer drug, but like most drugs, the effect varies from person to person. This is partly due to a variation in how well each person eradicates the drug from the body. This can lead to toxicity if the drug is eliminated slowly. Just as important is inadvertent underdosing in people who eliminate the drug quickly which may lead to a reduced anti-cancer effect. The investigators group has developed a battery of tests that may measure how an individual clears a drug from their body. The investigators intend to apply these tests to a group of patients taking sunitinib to see whether any test will help predict the level of sunitinib in the body and also the side effects. If a test seems to be promising from this study it may be possible to do a simple test on patients before they receive sunitinib so the best dose is chosen. The tests involve identifying the genes that are involved with drug elimination (CYP3A, ABCB1, ABCG2, OCT1, OATP) as well as directly measuring elimination using marker drugs (midazolam clearance and sestamibi liver clearance).