Can a new drug make hormone therapy work better for breast cancer?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Able to understand study procedures, voluntarily participate in the study, and provide written informed consent. * Female patients aged ≥18 and ≤70 years with histopathologically confirmed untreated unilateral primary invasive breast cancer. * Hormone-receptor positive (estrogen receptor immunohistochemical expression ≥10%), and HER2-negative (IHC 0-1+, or IHC 2+ with negative FISH test). * Tumor size \>2 cm or positive regional lymph nodes (TNM stage II-IIIA). * At least one measurable target lesion according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. * Eastern Cooperative Oncology Group (ECOG) performance status 0-1. * Adequate cardiac function meeting all of the following criteria: i. 12-lead electrocardiogram shows no abnormality or clinically insignificant changes requiring no medical intervention; ii. QTc interval ≤480 ms; iii. No history of torsades de pointes or other symptomatic QTc abnormalities; iv. Left-ventricular ejection fraction (LVEF) ≥50%. * Adequate bone-marrow reserve: white blood cell count ≥3.0×10⁹/L; absolute neutrophil count ≥1.5×10⁹/L; platelet count ≥100×10⁹/L; hemoglobin ≥90 g/L. * Adequate hepatic and renal function: AST and ALT ≤2.5 × upper limit of normal (ULN); alkaline phosphatase ≤2.5 × ULN; total bilirubin ≤1.5 × ULN; serum creatinine ≤1.5 × ULN. * For pre-menopausal females or females without surgical sterilization: agree to use effective contraception during study treatment and for at least 6 months after the last dose of study treatment. Exclusion Criteria: * Occult breast cancer, inflammatory breast cancer, Paget's disease of the breast, stage IV (metastatic) breast cancer, or bilateral breast cancer. * Known hypersensitivity to active ingredients or other excipients of study drugs. * Requirement for additional anti-tumor therapy (excluding ovarian function suppression) during neoadjuvant treatment, as judged by the investigator. * Prior hormone-replacement therapy that has not been discontinued for at least 2 weeks before study treatment initiation. * Previous history of anti-tumor chemotherapy, selective estrogen-receptor modulators, or aromatase inhibitor therapy. * Severe cardiac diseases or conditions that would preclude tolerability of study treatment, including but not limited to: i. Life-threatening arrhythmias or higher-grade atrioventricular block (Mobitz type II second-degree or third-degree atrioventricular block); ii. Unstable angina pectoris; iii. Clinically significant valvular heart disease; iv. Electrocardiogram evidence of transmural myocardial infarction; v. Poorly controlled hypertension. * Major surgery unrelated to breast cancer within 4 weeks prior to enrollment, or incomplete recovery from such surgical procedures. * Severe or uncontrolled infections that may interfere with study treatment or outcome assessment, including but not limited to active viral hepatitis, positive human immunodeficiency virus antibody, pulmonary infection. * History of other malignancies within the past 5 years (except cured carcinoma in-situ of cervix or basal-cell carcinoma of skin). * Underlying gastrointestinal disorders (especially chronic diarrhea or constipation), inability to swallow, intestinal obstruction, or other conditions interfering with drug intake and absorption. * Any other condition rendering the patient unsuitable for study participation, in the investigator's opinion