ARX788 in HER2-positive Metastatic Breast Cancer Patients

Inclusion Criteria: * 18 to 75 years old (including upper and lower limits), male or female; * Unresectable locally advanced, recurrent or metastatic BC; * Has previously received ≤ two lines of chemotherapy (excluding hormone therapy) for recurrent or metastatic BC; * Tissue samples determined to be HER2 positive (defined as IHC3+ or FISH+); * Has at least one measurable target lesion as per RECIST1.1 criteria; * Has recovered from any AE (≤ Grade 1) related to prior surgery and prior cancer treatment; * Adequate bone marrow, liver, kidney and coagulation function; * ECOG Performance Status Score of 0-1; * Voluntarily sign the informed consent, have good compliance and are willing to comply with the follow-up visit. Exclusion Criteria: * Has known history to be allergic to any active ingredient or excipient of ARX788; * With meningeal metastases or disseminated brain metastases or active brain metastases, who need radiation, surgery or drug therapy; * Has pericardial effusion, pleural effusion or ascites effusion with clinical symptoms, signs or require symptomatic treatment; * Has interstitial lung disease requiring steroid therapy, a history of drug-induced interstitial lung disease, a history of radiation pneumonitis, or any evidence indicating clinically active interstitial lung disease; * Has any eye disease that require medical intervention such as keratitis, corneal diseases or active eye infection; * Has cardiac insufficiency; * Uncontrolled hypertension; * Has evidence of severe or uncontrollable systemic diseases; * Received live vaccines within 4 weeks before the first use of the investigational product or plans to receive live vaccines during the trial; * Breastfeeding female, or who has childbearing potential with a positive baseline pregnancy test or who is unwilling to use effective contraception during the trial; * Is unwilling or unable to stop wearing corneal contact lens during the trial; * Has received any systemic anti-tumor therapy (with the exception of endocrine therapy, with an interval of at least 7 days) within 28 days (or at least 5 half-lives) before the first use of the investigational product; * Has any mental or cognitive disorder that may restrict his/her understanding and execution of the informed consent form; * Other conditions that the Investigator considers inappropriate for participation in this trial, such as poor compliance.