• ECOG physical condition 0-1 point.

• Advanced unresectable or metastatic breast cancer confirmed by histopathology or cytopathology.

• Menopausal Status.

• Previous treatments: (New) adjuvant endocrine therapy combined or not combined with CDK4/6 inhibitors during or within 12 months after treatment, including recurrence/metastasis, shall be counted as one line of endocrine therapy and one line of CDK4/6 inhibitor therapy (such as combined CDK4/6 inhibitors); Relapse/metastasis during (new) adjuvant chemotherapy or within 6 months after the end of treatment (whichever occurs later), counted as one line of chemotherapy.

• Disease progression confirmed by imaging during or after the last systemic anti-tumor treatment before the first use of medication (limited to the stage of efficacy expansion).

• There must be at least one measurable extracranial lesion that meets RECIST v1.1 at baseline.

• Expected survival\>3 months.

• The functional level of 8 organs is good.

• Previous treatments: The interval between receiving nitrosourea or mitomycin C before the first medication in this study was ≥ 6 weeks; Receiving cytotoxic drugs, endocrine therapy, immunotherapy, targeted therapy, surgical interval (excluding biopsy or PICC catheterization or PORT infusion port catheterization surgery), or other clinical studies with the last dose of medication ≥ 4 weeks; The interval between the end of radiotherapy is ≥ 2 weeks.

⁃ female participants with fertility must agree to use efficient contraceptive measures for contraception during the study treatment period and within 7 months after the end of the study treatment period; Female subjects with fertility must have a negative serum HCG test within 7 days prior to enrollment in the study and must be non lactating.

⁃ Voluntarily participate in this clinical trial, willing and able to comply with the clinical visit and research related procedures, understand the research procedures, and have signed informed consent.