• 1\. The subject is able to understand the informed consent form, voluntarily participate and sign the informed consent form.

• 2\. The subject ≥ 18 years old on the day of signing the informed consent form, male or female.

• 3\. Unresectable locally recurrent or metastatic breast cancer, previous histopathological reports of HER2 IHC 1+ or 2+ and ISH-, previous histopathological reports have not been diagnosed as HER2 IHC 3+ or 2+ and ISH+.

• 4\. Have received at least 1 to 2 lines of chemotherapy regimens for breast cancer in the relapse/metastatic stage.

• 5\. Willing to provide sufficient archived tumor pathology specimens for central laboratory detection of HER2 status.

• 6\. Documented radiographic disease progression (during or after the most recent treatment).

• 7\. At least one extracranial measurable lesion at baseline according to RECIST 1.1 criteria.

• 8\. Expected survival ≥ 3 months. 9. ECOG score of 0 or 1 within 14 days prior to administration. 10. Female subjects of childbearing potential or male subjects of fertile partner consent to use highly effective contraception from the signing of informed consent.

• 11\. Laboratory tests within 14 days before administration and cardiac function tests within 28 days meet the criteria.

• 12\. Have sufficient elution of previous treatment before administration.