Using a prospective, exploratory trial design, we aim to evaluate the efficacy and safety of RC-Trastuzumab combined with Rilafup Alpha in treating first-line systemically treated HER2（Human Epidermal Growth Factor Receptor 2 ） medium-to-high expressing gastric/gastroesophageal junction adenocarcinoma that has failed standard therapy. Participants, after being fully informed and signing the consent form, and passing the screening, enter the treatment phase. The trial medications include RC-Trastuzumab and Rilafup Alpha: RC-Trastuzumab: 4.8 mg/kg i.v.gtt on day 1, every 3 weeks; continue until disease progression, intolerance, or study withdrawal. Rilafup Alpha: 1800 mg or 30 mg/kg i.v.gtt on day 1, every 3 weeks; continue until disease progression, intolerance, or study withdrawal, with a maximum treatment duration of 2 years.
Efficacy assessment: Imaging is done every 2 cycles from the start of therapy until the end of treatment, consent withdrawal, or death. If participants leave the study for any reason and no imaging has been done within 4 weeks before stopping treatment, imaging should be performed at exit. Participants with CR or PR are to have a repeat imaging evaluation 4 weeks later for confirmation. According to RECIST(Response Evaluation Criteria in Solid Tumors version ) 1.1 criteria, for those showing initial PD but clinically stable, confirmation should be done after a 4-week interval, and imaging resumes at the next scheduled time point.
Additionally, the study evaluates drug safety and survival. Safety assessment: Adverse events are graded according to NCI-CTCAE(National Cancer Institute Common Terminology Criteria for Adverse Events) 6.0. During the trial, adverse events should be recorded accurately, including onset, severity, relation to study drugs, duration, actions taken, and outcome. Survival assessment: The follow-up period starts after the last dose of study drug. The study center conducts follow-ups every 3 months during the first year after treatment, then every 6 months, until death or study completion. Follow-ups by phone are acceptable.