Effects of Tucatinib on Cardiac Repolarization in Healthy Participants

This study will evaluate the effects of a steady state therapeutic dose of tucatinib on QTcF (QT interval corrected for heart rate using Fridericia's method) in healthy individuals. In this design, study treatment will be dosed in 3 sequential treatment periods: Treatment A: Oral doses of 300mg tucatinib for 5 days Treatment B: Oral doses of matching placebo for tucatinib for 5 days Treatment C: A single oral dose of 400 mg of moxifloxacin Patients will be randomized based on 2-Williams-square design to 1 of 6 treatment sequences to maintain the study blind for tucatinib and placebo.