A Safety Study of Tucatinib in Healthy and Hepatically-Impaired Subjects

Inclusion Criteria: * In good general health, except for additional inclusion criteria related to subjects with hepatic impairment * Within body mass index (BMI) range of 18 to 37 kg/m\^2 (inclusive) * Males capable of fathering a child must agree to use contraception from check in through 90 days after dose administration * Females must be of nonchildbearing potential * Able to understand and provide written informed consent * Able to comply with all study procedures, including the 3-night stay at the clinical site and follow-up phone call * Healthy subjects only: matched to subjects with Mild and/or Moderate and/or Severe hepatic impairment in sex, age (+/- 10 years), and BMI (+/- 20%). * Hepatic impairment subjects only: considered to have Mild, Moderate, or Severe hepatic impairment that has been clinically stable for at least 1 month * Hepatic impairment patients only: currently on stable medication regimen Exclusion Criteria: * Subjects with at-rest vital signs outside of the following ranges: heart rate (40 to 120 bpm), systolic blood pressure (90 to 150 mmHg), diastolic blood pressure (40 to 95 mmHg) * Clinically significant abnormal laboratory values or physical examination findings * Evidence/history of long QT syndrome * Use of drugs/substances known to be inhibitors or inducers of CYP3A4 or CYP2C8 enzyme within 30 days * Consumption of foods or beverages containing poppy seeds, grapefruit, or Seville oranges within 7 days of check-in * Consumption of alcohol-, citric acid-, caffeine-, or xanthine-containing foods or beverages within 48 hours prior to check in * Subjects with known alcohol and/or drug abuse within 1 month prior to check in * History of significant hypersensitivity, intolerance, or allergy to any drug compound, food, or other substance * History of congenital nonhemolytic hyperbilirubinemia * History of stomach or intestinal surgery that would potentially alter absorption and/or excretion of orally administered drugs * Prior doses of tucatinib * Prior dose of any investigational drug within the past 30 days or 5 half-lives