Inclusion Criteria:
1. Initially diagnosed with stage II-III breast cancer according to the AJCC 8th edition staging system.
2. Premenopausal or perimenopausal patients (who must receive ovarian function suppression \[OFS\], including bilateral oophorectomy or GnRHa \[GnRH agonists\]), or postmenopausal patients.
3. Histopathologically confirmed HR+/HER2- breast cancer: estrogen receptor (ER)-positive (\>10%), regardless of progesterone receptor (PR) expression level; HER2-negative invasive breast carcinoma as per the 2018 ASCO-CAP HER2-negative interpretation guidelines, confirmed by the pathology laboratory as immunohistochemistry (IHC) 0, 1+, or 2+ with negative in situ hybridization (ISH) (HER2/CEP17 ratio \<2.0).
4. Female patients aged 18-75 years (inclusive).
5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
6. Life expectancy ≥12 weeks.
7. At least one measurable lesion according to RECIST version 1.1.
8. Adequate organ function as defined by:
Hematology: absolute neutrophil count (ANC) \>=1.5×10⁹/L; platelet count (PLT) ≥100×10⁹/L; hemoglobin (Hb) \>=90 g/L.
Blood biochemistry: total bilirubin (TBIL) =\<1.5× upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) =\<3×ULN; blood urea nitrogen (BUN) and creatinine (Cr) =\<1.5×ULN, and creatinine clearance \>=50 mL/min.
9.12-lead electrocardiogram (ECG) with QTc interval ≤480 ms. 10.Willing to voluntarily participate, provide written informed consent, and comply with study visits and follow up.
Exclusion Criteria:
1. Prior receipt of any form of anti tumor therapy (including chemotherapy, radiotherapy, molecularly targeted therapy, endocrine therapy, etc.).
2. Concurrent use of other anti tumor drugs.
3. Stage IV breast cancer.
4. Breast cancer not confirmed by histopathology.
5. Other malignancies within the past 5 years, except for cured cervical carcinoma in situ, basal cell carcinoma, or squamous cell carcinoma of the skin.
6. Severe dysfunction of vital organs such as heart, liver, or kidneys.
7. Inability to swallow, chronic diarrhea, or intestinal obstruction, or any condition that may affect oral drug absorption.
8. Participation in another drug clinical trial within 4 weeks prior to enrollment.
9. History of immunodeficiency, including positive HIV test, positive HCV antibodies, active hepatitis B virus infection (HBsAg positive with detectable HBV DNA), or other acquired/congenital immunodeficiency diseases, or history of organ transplantation.
10. Known hypersensitivity to any component of the study drugs.
11. Any cardiac disease, including: arrhythmia requiring medication or clinically significant; myocardial infarction; heart failure; or any other cardiac condition deemed by the investigator as unsuitable for participation.
12. Pregnant or breastfeeding women, or women of childbearing potential with a positive baseline pregnancy test.
13. Concurrent medical conditions that, in the investigator's judgment, may compromise patient safety or interfere with study completion (including but not limited to severe hypertension not controlled by medication, severe diabetes, active infections, etc.).
