Exclusion criteria

• Untreated brain metastases or brain metastases requiring steroids above physiologic replacement doses
• Prior treatment with ARV-471
• Prior treatment targeting mTOR (e.g. everolimus)
• Prior anticancer or investigational drug treatment within 28 days (fulvestrant) or 14 days (tamoxifen or aromatase inhibitor, or CDK 4/6 inhibitor) before the first dose of study drug
• Prior anticancer or investigational anticancer drug therapy within 28 days or 5 half-lives (whichever is shorter) before the first dose of study drug, except as mentioned above
• Any of the following in the previous 12 months: myocardial infarction, severe/unstable angina, coronary/peripheral artery bypass graft, symptomatic congestive heart failure, cerebrovascular accident, transient ischemic attack, symptomatic pulmonary embolism, or other clinically significant episode of thromboembolism
• Any of the following in the previous 6 months: congenital long QT syndrome, Torsade de Pointes, sustained ventricular tachyarrhythmia and ventricular fibrillation, left anterior hemiblock, ongoing cardiac arrythmias/dysrhythmias, atrial fibrillation
• Hypertension that cannot be controlled by medication (\>150/90 mmHg despite optimal medical therapy)
• Active, uncontrolled bacterial, fungal, or viral infection, including hepatitis B virus, hepatitis C virus, known human immunodeficiency virus (HIV), or acquired immunodeficiency syndrome (AIDS)-related illness
• Known history of drug-induced pneumonitis or other significant symptomatic deterioration of lung function
• Live vaccines within 14 days before the first dose of study drug
• Major surgery (as defined by the Investigator) within 4 weeks of first dose of study drug
• Radiation therapy within 4 weeks of first dose of study drug or prior irradiation to more than 25% of the bone marrow