A Study of XZP-3287 in Combination With Letrozole/Anastrozole in Patients With Advanced Breast Cancer

Inclusion Criteria: 1. Female patients aged ≥18 years and ≤75 years old; 2. Patient is in the menopausal state； 3. Histologically or cytologically confirmed locally advanced, recurrent or metastatic breast cancer, which was pathologically confirmed to be HR-positive and HER2-negative; 4. Evidence of locally advanced, recurrent, or metastatic disease that is not amenable to curative surgical resection or radiation therapy and is not clinically amenable to chemotherapy; 5. No prior systemic anticancer therapy for locally advanced, recurrent, or metastatic disease; 6. At least one measurable lesion (based on RECIST v1.1) or only bone metastases; 7. Patient has an Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1; 8. Adequate organ and marrow function; 9. Patient of childbearing age must undergo a serum pregnancy test within 7 days before randomization, and the result is negative; patient is willing to use a medically approved high-efficiency contraceptive method during the study period and within 6 months after the last study drug treatment; 10. Patient with acute toxic reactions caused by previous anti-tumor treatments or surgical operations were alleviated to grade 0 to 1 (NCI-CTCAE v5.0), or to the level specified by the enrollment criteria; 11. Patient has signed informed consent before any trial related activities. Exclusion Criteria: 1. Patients with disease recurrence or metastasis at or within 12 months after previous neoadjuvant or adjuvant therapy with endocrine drugs; 2. Patient with visceral crisis or brain metastases, except for patient with stable brain metastases; 3. Patient had clinically significant pleural effusions, ascites effusions, or pericardial effusions in the 4 weeks before enrollment; 4. Patient who received prior treatment with mTOR inhibitors or CDK4/6 inhibitors ; 5. Participation in a prior treatment of major surgery, chemotherapy, radiotherapy, and any anti-tumor treatment within 14 days before enrollment； 6. Patient who participated in other clinical trials within 14 days before enrollment or within 5 half-lives of the trial drug, whichever is longer; 7. Patient used CYP3A4 potent inhibitors or potent inducers within 14 days before enrollment or within 5 half-lives of the drug, whichever is longer; 8. Initiation of bisphosphonates or RANKL inhibitors within 7 days before enrollment, and subjects who have initiated treatment \> 7 days before enrollment should not change the method of use; 9. Any other malignant tumor has been diagnosed within 5 years before randomization; 10. Patient is in the active stage of HBV, HCV or co-infected with HBV, HCV, or Patient with positive HIV antibody; 11. Patient with severe infection within 4 weeks before enrollment, or unexplained fever\> 38.3℃ during screening/before enrollment; 12. Patient with heart function impaired or clinically significant heart disease within 6 months before enrollment; 13. Cerebrovascular accident occurred within 6 months before enrollment, including history of transient ischemic attack or stroke; pulmonary embolism; 14. Inability to swallow, intestinal obstruction or other factors that affect the taking and absorption of the drug; 15. Patient with a known hypersensitivity to any of the excipients in this study; 16. A prior history of autologous or allogeneic hematopoietic stem cell transplantation; 17. A prior history of psychotropic drug abuse or drug use; 18. Nursing Mothers; 19. The researchers considered that there were some cases that were not suitable for inclusion.