This study evaluated the safety and efficacy of SPH4336 in combination with endocrine therapy in the treatment of locally advanced or metastatic breast cancer that progressed on CDK4/6 inhibitor combined with endocrine therapy.

Inclusion Criteria:

1. Patients who voluntarily participate in this study, completely understand this study, and voluntarily sign the informed consent form (ICF).
2. ECOG (Eastern Cooperative Oncology Group) performance status score of 0 or 1.
3. Life expectancy ≥ 3 months.
4. Patients with locally advanced or metastatic breast cancer who are unable to receive radical surgeries/other local therapies.
5. At least one measurable lesion.
6. Laboratory test results meet the relevant requirements for organ function.
7. Subjects who agree to take effective contraceptive measures.

Exclusion Criteria:

1. Inflammatory breast cancer.
2. Patients unsuitable for endocrine therapy at the investigator's discretion.
3. History of other malignancies prior to the start of study treatment.
4. Patients with known metastases to central nervous system.
5. Taking anti-tumor traditional Chinese patent medicines at the time of signing the ICF.
6. Patients who underwent a surgery prior to the start of study treatment, and have not yet recovered from adverse reactions of the surgery.
7. Patients who participated in a clinical trial and received other investigational drugs before the start of study treatment.
8. Pregnant or lactating women.
9. History of myocardial infarction, unstable angina pectoris, severe arrhythmia, and symptomatic congestive heart failure before the start of study treatment; ≥ NYHA (New York Heart Association) Class II; mean QTc interval ≥ 470 ms before the start of study treatment; left ventricular ejection fraction ≤ 50% before the start of study treatment.
10. History of ischemic stroke or severe thromboembolic disease before the start of study treatment.
11. Hepatitis B surface antigen positive and HBV (Hepatitis B Virus) DNA > 2,000 IU/mL or > 104 copies/mL; HCV (Hepatitis C Virus) antibody positive and HCV RNA positive; or known HIV infection.
12. History of severe allergic diseases, history of severe drug allergies, or known allergy to any ingredient of the investigational product.
13. Presence of diseases or conditions that may impact drug administration or gastrointestinal absorption before the start of study treatment.
14. Presence of uncontrolled infections before the start of study treatment.
15. Known history of drug abuse, excessive drinking, or illegal drug use; history of confirmed neurological or mental disorders.
16. Presence of other diseases that the risks of receiving the study treatment outweigh its benefits, as determined by the investigator, or any other reason for which patients are ineligible for the study as assessed by the investigator.

Female