A Study to Learn How the Study Medicine Called Atirmociclib is Handled by the Body in People With Normal Liver Function and Different Levels of Liver Disease

The purpose of this study to understand how the study medicine atirmociclib behaves in the body and how safe it is for people with different levels of liver health. The study is seeking participants who are: * Aged 18 years or older * Have a BMI of 17.5 to 40 kg/m2, and body weight more than 50 kg. * Have normal liver function or have stable mild, moderate, or severe liver disease Participants will receive study medicine by mouth. Blood samples will be collected to see how much of the medicine is in the body over time. This will help understand whether liver disease changes how the medicine is handled. Participants will be in the study for about 9 weeks. Those with normal liver function will stay in the clinic for about 7 days. People with liver disease will stay for about 9 days. After leaving the clinic, people may be contacted for follow-up. This may be done by phone or through a clinic visit.