Select the Appropriate Population for Adding CDK4/6i to Neoadjuvant Endocrine Therapy

Inclusion Criteria:

1. Newly treated female patients, ≥18 and ≤75 years;
2. ECOG score 0-1;
3. Breast cancer following:

   Histologically confirmed invasive breast cancer with primary tumor diameter \>2 cm by standard evaluation methods.Tumor stage: cT2-cT4/cN0-cN3/cM0 (clinical phase II and III)
4. HR+/HER2- breast cancer confirmed by pathological examination, defined as: primary HR+/HER2- breast cancer performed by the pathology department of the Central Hospital;
5. Get hormone receptor status (ER and PR);
6. Major organ function following:

   Complete blood count: Neutrophil (ANC) ≥ 1.5×109/L; Platelet count (PLT) ≥ 90×109/L; hemoglobin (Hb) ≥90 g/L; Blood Biochemistry: Total bilirubin (TBIL) ≤ 2.5×ULN; Alanine aminotransferase (ALT) ≤ 1.5×ULN; Aspartate aminotransferase (AST) ≤ 1.5×ULN; Alkaline phosphatase ≤ 2.5×ULN; Urea nitrogen (BUN) ≤ 1.5×ULN; Creatinine (Cr) ≤ 1.5×ULN; Twelve-lead electrocardiogram: Fridericia corrected QT Interval (QTcF) woman \< 470 ms (QTcF=QT/(RR\^1/3));
7. Woman who are not menopausal or have not been surgically sterilized agree to abstain from sex or use effective contraceptive methods for at least the duration of the study treatment and for 7 months after the last dosing;
8. Volunteer to participate in the study, sign informed consent, have good compliance and be willing to cooperate with follow-up.

Exclusion Criteria:

1. IV stage breast cancer or metastatic breast cancer;
2. Inflammatory breast cancer;
3. Any previous malignant tumor or previous anti-tumor therapy or radiotherapy were not allowed, excluding cured cervical carcinoma in situ, basal cell carcinoma or squamous cell carcinoma;
4. Participate in other clinical trials;
5. Patients were not allowed who had undergone major non-breast cancer related surgery within 4 weeks prior to randomization or had not fully recovered from such surgery;
6. Patients were not allowed who had received blood transfusion or colony stimulating factor treatment within 2 weeks before randomization;
7. Patients were not allowed who allergic to drug components;
8. Patients were not allowed who had a history of immunodeficiency, including HIV positive, or other acquired, congenital immunodeficiency diseases, or a history of organ transplantation;
9. Patients have heart disease were not allowed including: (1) angina pectoris; (2) medically treatable or clinically significant arrhythmias; (3) myocardial infarction; (4) heart failure; (5) any other heart disease that the investigator has determined is not suitable for participation in the study;
10. Pregnant and lactating women, fertile women who tested positive for baseline pregnancy tests, or fertile women who were unwilling to take effective contraceptive measures during the test period were not allowed;
11. Patients have concomitant diseases that endanger patient safety or influence the completion of the study were not allowed (including but not limited to hypertension, severe diabetes, active infection, thyroid disease, etc.);
12. Patients were not allowed who with inability to swallow, chronic diarrhea and intestinal obstruction, accompany multiple factors affecting the administration and absorption of medicines;
13. Any other circumstances in which the investigator considers the patients unsuitable for participation in the study.