A Drug-Drug Interaction Study in Healthy Volunteers of the Effects of Tucatinib

This study is being done to look at how tucatinib could affect the way other drugs work. This study will look at healthy volunteers and how tucatinib affects their liver enzymes. Liver enzymes can change how drugs work in the body. There are 5 parts to this study. Parts A and C are looking at how the body breaks down tucatinib when there are lower levels of certain liver enzymes. Part B is looking at how the body breaks down tucatinib when there are high levels of certain liver and stomach enzymes. Parts D and E are looking at how tucatinib could change the levels of some liver and stomach enzymes in the body. This will help us know more about how tucatinib should be given to patients.