A Phase II study to evaluate the safety, tolerability, pharmacokinetics, and efficacy of IBI343 in combination therapy for patients with advanced malignant solid tumors.To evaluate the efficacy and safety of IBI343 in combination therapy for patients with advanced malignant solid tumors.Enrollment of subjects with advanced gastric/gastroesophageal junction adenocarcinoma positive for CLDN18.2, and subjects with pancreatic ductal adenocarcinoma positive for CLDN18.2.

Inclusion criteria:

1. Signed written informed consent, willing and able to comply with the protocol-specified visits and related procedures.
2. At least one measurable lesion according to the Response Evaluation Criteria in Solid Tumors (RECIST v1.1).
3. Age ≥ 18 years, no gender restrictions.
4. An Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1.
5. Expected survival ≥ 12 weeks.
6. Adequate bone marrow and organ function.
7. Female subjects of childbearing potential or male subjects whose partners are of childbearing potential must use effective contraception throughout the treatment period and for 6 months after the end of treatment.
8. Confirmed CLDN18.2 positive by central laboratory pathological tissue testing.

Exclusion criteria:

1. Currently participating in another interventional clinical study, except for observational (non-interventional) clinical studies or those in the survival follow-up phase of an interventional study.
2. Received treatment with a strong cytochrome P450 3A4 (CYP3A4) inhibitor within 2 weeks or 5 half-lives (whichever is longer) prior to the first dose of the investigational drug.
3. Received the last anti-tumor treatment within 4 weeks or 5 half-lives of the anti-tumor therapy (whichever is shorter) before the first dose of the investigational drug.
4. Received therapeutic or palliative radiotherapy within 2 weeks prior to the first dose of the investigational drug.
5. Underwent biliary stent placement within 7 days prior to the first dose of the investigational drug.
6. Planning to receive other anti-tumor treatments during the period of treatment with the investigational drug.
7. Received any live vaccine within 4 weeks prior to the first dose of the investigational drug or planning to receive any live vaccine during the study.
8. Underwent major surgery within 4 weeks prior to the first dose of the investigational drug, or has unhealed wounds, ulcers, or fractures; or plans to undergo major surgery during the study.
9. Has not recovered from toxicity caused by previous treatment to grade 0 or 1 according to NCI CTCAE v5.0 prior to the first dose of the investigational drug.
10. History of gastrointestinal perforation and/or fistula within 6 months prior to the first dose of the investigational drug that was not cured by surgical treatment.
11. Presence of pyloric obstruction and/or persistent recurrent vomiting.
12. Post-procedure of stent implantation in the digestive tract or trachea.
13. Symptomatic central nervous system metastasis.
14. Bone metastasis with risk of paraplegia.
15. Interstitial lung disease requiring steroid treatment, or history of interstitial lung disease, non-infectious pneumonia, severe impairment of pulmonary function, or uncontrolled pulmonary disease such as pulmonary fibrosis, severe radiation pneumonitis, acute lung injury, etc., or suspected of having these diseases during the screening period.
16. Presence of uncontrolled disease.
17. History of other primary malignant tumors.
18. Known history of immunodeficiency.
19. History of allogeneic organ transplantation and allogeneic hematopoietic stem cell transplantation.
20. Previous treatment with topoisomerase inhibitor-based antibody-drug conjugates.
21. For subjects receiving drug treatment, a history of allergy to the corresponding drug or formulation.
22. For subjects receiving drug treatment, contraindications for the corresponding drug.
23. For subjects receiving drug treatment, a history of permanent discontinuation of the corresponding drug due to related adverse reactions.
24. Pregnant or lactating female subjects.
25. Other conditions deemed unsuitable for participation in this study by the investigator.