Inclusion Criteria:
1. Women aged 18 to 75 years, either pre-menopausal/post-menopausal or post-menopausal.
2. Histologically confirmed HR+/HER2- locally advanced or metastatic breast cancer. Specific definition: Immunohistochemical detection of ER \> 10% positive tumor cells is defined as ER positive, PR \> 10% positive tumor cells is defined as PR positive, and ER and/or PR positive is defined as HR positive; HER2 0-1+ or HER2 ++ but negative after FISH detection without amplification is defined as HER2 negative;
3. Have not received any systemic treatment for local recurrence or metastatic diseases before.
4. Recurrence occurred more than 12 months after the completion of adjuvant endocrine therapy.
5. According to the RECIST 1.1 , at least one measurable lesion.
6. Eastern Cooperative Oncology Group (ECOG) physical condition score is 0-1.
7. The functional of organs are normal:
8. Pregnant women of childbearing age must have undergone a serum pregnancy test 28 days before enrollment, and the result is negative. patients are willing to use a medically approved highly effective contraceptive method during the study period and within 1 year after the last administration of the study drug.
9. Non-pregnant or non-lactating female patients.
10. Not participating in other ongoing studies .
11. With the consent of the patient or their legal representative and having signed the informed consent form, willing and capable of following the planned visits, study treatment plan, laboratory tests and other trial procedures.
Exclusion Criteria:
1. Any evidence of severe or uncontrollable systemic diseases, including active bleeding disorders, active infections (such as hepatitis B, hepatitis C and human immunodeficiency virus), or severe damage to bone marrow reserves or organ functions (such as liver and kidney damage).
2. Previous use of CDK4/6 inhibitors.
3. Active brain metastases or meningeal brain metastases.
4. Upper limb arterial blood pressure lower than 90/60 mmHg.
5. Any history of malignant tumors other than breast cancer within the past 5 years, excluding cured cervical carcinoma in situ, basal cell carcinoma of the skin or squamous cell carcinoma.
6. Severe pneumonia history such as interstitial pneumonia.
7. At the time of starting the study treatment, the patient has not recovered from any CTCAE ≥ 3 grade toxicity caused by previous treatment.
8. Had any heart disease, including: (1) requiring drug treatment or clinically significant arrhythmia; (2) myocardial infarction; (3) heart failure; (4) any other heart disease judged by the researcher or sponsor as not suitable for participating in this trial; etc.
9. Significant comorbidities, including mental disorders that the investigator or sponsor considers would adversely affect the patient's participation in the study.
10. History of immunodeficiency diseases, including positive HIV testing, or having other acquired or congenital immune deficiency diseases, or having a history of organ transplantation and allogeneic bone marrow transplantation; history of interstitial lung disease, non-infectious pneumonia.
11. Patients considered not suitable for inclusion by the investigator.
