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

Inclusion criteria including but not limited to: * BMI of 17.5-40 kg/m2; and a total body weight \>50 kg (110 lb). * Willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures. * Capable of giving signed informed consent. Normal hepatic function group only: \- Overtly healthy as determined by medical evaluations including medical history, physical examination, laboratory tests, vital signs and standard 12-lead ECGs. Hepatic impairment groups only: \- Stable hepatic impairment meeting the criteria for Child-Pugh Class A, B, or C . Stable hepatic impairment is defined as no clinically significant change in disease status within the last 28 days prior to the screening visit, as documented by the participant's recent medical history. Exclusion criteria including but not limited to: * Any condition or history of surgery possibly affecting drug absorption. * Use of prohibited prior or concomitant medications. Normal hepatic function group only: \- Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, psychiatric, neurological, or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at the time of dosing). Hepatic impairment groups only: \- A diagnosis of hepatic dysfunction secondary to any acute ongoing hepatocellular process that is documented by medical history, PE, liver biopsy, hepatic ultrasound, CT scan, or MRI.