This study is a multicenter, open-label, phase II clinical study to explore the safety and efficacy of BL-M07D1+PD-1 monoclonal antibody in patients with unresectable locally advanced or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma.

Inclusion Criteria:

1. Voluntarily sign the informed consent and follow the requirements of the protocol;
2. No gender limit;
3. Age ≥18 years old and ≤75 years old at the time of signing the informed consent;
4. Expected survival time ≥3 months;
5. Patients with HER2-positive gastric or gastroesophageal junction adenocarcinoma confirmed by pathology;
6. Patients provided tumor tissue specimens as far as possible for the detection of biomarkers such as HER2 and PD-L1 for exploratory retrospective analysis;
7. Must have at least one measurable lesion according to RECIST v1.1 definition;
8. ECOG 0 or 1;
9. Toxicity of previous antineoplastic therapy has returned to ≤ grade 1 defined by NCI-CTCAE v5.0;
10. No severe cardiac dysfunction, left ventricular ejection fraction ≥50%;
11. Blood transfusion is not allowed within 14 days before the first use of study drugs, and the use of colony-stimulating factors is not allowed, and the organ function level must meet the requirements;
12. Coagulation function: international normalized ratio (INR) ≤1.5 and activated partial thromboplastin time (APTT) ≤1.5×ULN;
13. Urine protein ≤2+ or ≤1000mg/24h;
14. Female subjects of childbearing potential, or male subjects with a fertile partner, had to use highly effective contraception from 7 days before the first dose until 7 months after the dose. Female subjects of childbearing potential had to have a negative serum pregnancy test within 7 days before the first dose.

Exclusion Criteria:

1. Anti-tumor therapy such as chemotherapy, biological therapy, and immunotherapy had been used within 4 weeks or 5 half-lives before the first dose. Oral drugs such as fluorouracil;
2. Prior ADC drug therapy with camptothecin derivative as toxin;
3. The history of severe cardiovascular and cerebrovascular diseases in the past six months;
4. Serious impairment of lung function due to pulmonary diseases;
5. QT prolongation, complete left bundle branch block, III degree atrioventricular block, frequent and uncontrollable arrhythmia;
6. Other primary malignancies diagnosed within 5 years before the first dose;
7. Poorly controlled hypertension;
8. A history of ILD requiring steroid therapy, current ILD/interstitial pneumonia or suspected to have such a condition during screening;
9. Patients with active central nervous system metastases;
10. Patients who are allergic to any excipients of the trial drug;
11. Systemic corticosteroids or immunosuppressive agents are required within 2 weeks before study dosing;
12. Patients with massive or symptomatic effusions or poorly controlled effusions;
13. Severe systemic infection within 4 weeks before screening;
14. Active autoimmune and inflammatory diseases;
15. Human immunodeficiency virus antibody positive, active hepatitis B virus infection or hepatitis C virus infection;
16. Previous history of allogeneic stem cell, bone marrow or organ transplantation;
17. A history of severe neurological or psychiatric illness;
18. Pregnant or lactating women;
19. The presence of other serious physical or laboratory abnormalities or poor compliance may increase the risk of participating in the study risk, or interference with the results of the study, and patients who were deemed by the investigators to be unsuitable for participation in the study.