Study of KN026 Monotherapy or Combination Therapy in Patients With Metastatic Breast Cancer

Inclusion Criteria: * Male or female subject \>= 18 years * Histologically/cytologically confirmed, locally advanced unresectable or metastatic breast cancer * ECOG score 0 or 1 * Life expectancy \>3 months * According to the definition of RECIST1.1, the patient has at least one measurable lesion * Adequate organ function prior to start treatment with KN026 * Able to understand, voluntarily participate and willing to sign the ICF Exclusion Criteria: * Accepted any other anti-tumor drug therapies within 4 weeks before fist dose * Accepted radiotherapy within 4 weeks before enrollment * Subjects are eligible with clinically controlled and stable neurologic function \>= 4 weeks, which is no evidence of CNS disease progression; Subjects with spinal cord compression and cancerous meningitis are not eligible * Pregnant or nursing females；or intend pregnancy within this study period or within 6 monthes after the end of this study * History of immunodeficiency, including HIV positive or other acquired, congenital immunodeficiency disease, or a history of organ transplantation * History of immunodeficiency, including HIV positive or other acquired, congenital immunodeficiency disease, or a history of organ transplantation * Cavity effusion (pleural effusion, ascites, pericardial effusion, etc.) are not well controlled, and need locally treatment or repeated drainage