JSKN003 Versus Treatment Of Physician'S Choice For HER2-low, Unresectable and/or Metastatic Breast Cancer Subjects

Inclusion Criteria:

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

2. The subject ≥ 18 years old on the day of signing the informed consent form, maleor female.

3. Unresectable locally recurrent or metastatic breast cancer, previoushistopathological reports of HER2 IHC 1+ or 2+ and ISH-, previous histopathologicalreports 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 inthe relapse/metastatic stage.

5. Willing to provide sufficient archived tumor pathology specimens for centrallaboratory detection of HER2 status.

6. Documented radiographic disease progression (during or after the most recenttreatment).

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

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

9. Laboratory tests within 14 days before administration and cardiac function testswithin 28 days meet the criteria.

10. Have sufficient elution of previous treatment before administration.

Exclusion Criteria:

• 1. Untreated, or unstable brain parenchymal metastases, spinal cord metastases orcompression, cancerous meningitis.

2. Patients with only skin lesions as target lesions. 3. Those with a history ofother primary malignant tumors within 5 years before administration.

3. Selection of the control drug by the investigator who is not suitable for theprotocol prescribed.

4. Previous use of antibody conjugates containing topoisomerase I inhibitors. 6.There is a third gap fluid that cannot be controlled by drainage, etc. 7. Previousor current interstitial pneumonia/lung disease requiring systemic hormone therapy.

5. Inability to swallow, chronic diarrhea, intestinal obstruction, or other factorsthat affect oral administration and absorption of the drug.

6. Previous or current autoimmune disease. 10. Have uncontrolled comorbidities. 11.The toxicity of previous antitumor therapy has not been restored to grade ≤1 (NCI-CTCAE v5.0).

7. History of previous immunodeficiency. 13. History of life-threatening allergicreactions or known ≥ grade 3 allergy to any component or excipient in theinvestigational pharmaceutical formulation.

8. Other conditions that the investigators believe will affect the safety oradherence to drug treatment in this study, including but not limited to psychiatricdisorders, alcohol or drug abuse.