Study on Using Circulating Tumor DNA to Predict Early Treatment Changes for Patients with Stage IV Breast Cancer

Inclusion Criteria

• Adults aged 18 or older.
• Diagnosed with ER+, HER2- metastatic (Stage IV) breast cancer.
• Have tumor tissue samples available.
• Have advanced breast cancer that cannot be cured, even if it has returned after previous treatment.
• No prior systemic treatment for advanced cancer, except for certain hormone therapies started less than 30 days before the study.
• No severe organ damage or blood issues.
• Have measurable cancer or cancer that can be evaluated.
• Good overall health with an ECOG score of 0 or 1.
• Able to understand and sign a consent form.
• Life expectancy of more than 3 months.
• Postmenopausal women or women with controlled ovarian function, or men, willing to use hormone therapy during the study.
• Resolved any side effects from previous cancer treatments to a mild level.

Exclusion Criteria

• Currently or recently treated for another cancer, except for certain skin or in situ cancers.
• Previous use of CDK4/6 inhibitors within 12 months before joining the study.
• Use of experimental drugs within 28 days before the study.
• Any condition that could interfere with the study or is not in the patient's best interest.
• Breast cancer that can be treated with curative intent.
• HER2+ tumor status.
• Prior hormone therapy in the metastatic setting unless started less than 30 days before the study.
• Negative or undetectable ctDNA levels at study entry.
• Recent major surgery or significant injury.
• Active bleeding disorders.
• Serious health conditions that conflict with the study.
• Difficulty swallowing tablets or conditions affecting absorption.
• Uncontrolled brain metastases or related conditions.
• Allergies to study medications.
• Uncontrolled electrolyte imbalances.
• Recent use of certain medications affecting liver enzymes.
• Need for radiation therapy during the study.
• Participation in another drug trial within 3 months.
• Recent history of other cancers, except for multiple ER+ breast cancers.
• History of blood cancers.
• Pregnant or breastfeeding women, or those not using effective contraception.