A Study Comparing BL-M05D1 With the Investigator's Choice of Treatment Regimen in Patients With Claudin (CLDN)18.2-Positive Advanced Gastric Cancer or Gastroesophageal Junction Adenocarcinoma (GC/GEJC) Who Have Received Prior First-Line Treatment

Prior treatment

• Prior anti-tumor therapy;
• Any thrombotic event within 6 months before randomization;
• History of interstitial lung disease (ILD) treated with hormones, etc.;
• Concurrent pulmonary diseases resulting in clinically severe respiratory impairment;
• Severe infection, etc. occurring within 4 weeks before the first use of the study drug;
• Prior organ transplantation or allogeneic hematopoietic stem cell transplantation;

Other illness

• History of severe cardiovascular and cerebrovascular diseases;
• Active autoimmune diseases and inflammatory diseases;
• Diagnosis of other malignancies within 3 years before the first dose;
• Hypertension poorly controlled with two antihypertensive drugs;
• Patients with a history of allergy to recombinant humanized antibodies or human-mouse chimeric antibodies, or allergy to any excipient component of BL-M05D1;
• Positive human immunodeficiency virus antibody, active tuberculosis, active hepatitis B virus infection, or active hepatitis C virus infection;
• History of intestinal obstruction, inflammatory bowel disease, or extensive bowel resection, etc.;

Lab values

• QT interval prolongation, complete left bundle branch block, third-degree atrioventricular block, frequent and uncontrollable arrhythmias;
• Patients with poorly controlled blood glucose;
• Patients with other severe physical or laboratory abnormalities or poor compliance, etc., which may increase the risk of participating in the study, or interfere with the study results, and patients deemed unsuitable for participation in this study by the investigator.

Other

• Positive HER2 expression in tumor tissue;
• Patients with active central nervous system metastases;
• Patients with massive serous cavity effusion, or serous cavity effusion with symptoms, or poorly controlled serous cavity effusion;
• Imaging examinations indicating that the tumor has invaded or encased major vessels in the chest, neck, pharynx, etc.;
• Pregnant or breastfeeding women;
• Esophageal or gastric varices requiring intervention within the past three months, etc.;

• Voluntarily sign the informed consent form and comply with protocol requirements;
• No gender restriction;
• Age: ≥18 years and ≤75 years;
• Expected survival time ≥3 months;
• Pathologically confirmed locally advanced unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma;
• Patients who have failed prior first-line standard treatment, with evidence of definitive radiological progression;
• Able to provide archived or fresh tumor tissue;
• Have radiologically evaluable lesions according to RECIST 1.1 criteria;
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;
• Toxicity from prior antitumor therapy has recovered to ≤Grade 1 as defined by NCI-CTCAE v6.0;
• No severe cardiac dysfunction, left ventricular ejection fraction ≥50%;
• Organ function levels must meet the requirements;
• Urine protein ≤1+ or \<1000 mg/24 h;
• For premenopausal women of childbearing potential, a pregnancy test must be performed within 7 days before starting treatment; serum pregnancy testing must exclude pregnancy, and the participant must not be breastfeeding; all enrolled trial participants and their partners must agree to use adequate highly effective contraception throughout the entire treatment period and for 7 months (women) and 4 months (men) after treatment completion, and it is recommended that additional contraceptive methods be used concurrently.