A Study of RC48-ADC in Local Advanced or Metastatic Gastric Cancer Subjects With the Overexpression of HER2

Inclusion Criteria: * Voluntary agreement to provide written informed consent. * Male or female, Age ≥ 18 years and ≤ 80 years. * Predicted survival ≥ 12 weeks. * Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1. * All female subjects will be considered to be of child-bearing potential unless they are postmenopausal, or have been sterilized surgically.Female subjects of child-bearing potential must agree to use two forms of highly effective contraception. Male subjects and their female partner who are of child-bearing potential must agree to use two forms of highly effective contraception. * Willing to adhere to the study visit schedule and the prohibitions and restrictions specified in this protocol. * Adequate organ function. * Have had progression or intolerance following receipt of at least two systemic chemotherapy for advanced or metastatic disease. * HER2 overexpression defined as HER2 IHC 2+ or 3+. * Measurable disease according to RECIST 1.1. Exclusion Criteria: * Known hypersensitivity to Recombinant Humanized Anti-HER2 Monoclonal Antibody-MMAE Conjugate For Injection. * History of receiving any anti-cancer drug/biologic treatment within 4 weeks prior to trial treatment. * History of major surgery within 4 weeks of planned start of trial treatment. * Has received a live virus vaccine within 4 weeks of planned start of trial treatment. * Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation for the full duration of the trial, or is not in the best interest of the subject to participate, in the opinion of the treating investigator. * History of other malignancy within the previous 5 years, except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, or cancers with a similar curative outcome as those mentioned above. * Assessed by the investigator to be unable or unwilling to comply with the requirements of the protocol.