SHR-A1904 Compared With Investigator's Choice of Therapy in Claudin18.2 Positive Patitens With Second-line Advanced or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria:

1. Age 18 to 75 years old (including boundary values)

2. Volunteer to participate in this clinical study and sign informed consent;

3. ECOG score 0-1;

4. Expected survival ≥3 months;

5. Gastric or Gastroesophageal Junction Adenocarcinoma;

6. positive CLDN18.2 expression in tumor tissue;

7. There is at least one measurable or evaluable lesion that meets the RECIST 1.1criteria;

8. Adequate bone marrow and organ function.

Exclusion Criteria:

1. Received anti-tumor therapies such as chemotherapy, radiotherapy, biologicaltherapy, targeted therapy, or immunotherapy within 4 weeks before the first dose ofthe study

2. HER2 posotive (IHC 3+ or IHC 2+/ISH +);

3. Toxicities caused by previous anticancer therapy were not recovered to CTCAE 5.0Grade≤1;

4. Individuals with Leptomeningeal metastasis or Active brain metastases;

5. Individuals with a history of GI perforation or fistula, unstable GI bleeding;

6. Individuals with a history of severe cardiovascular and cerebrovascular diseases;

7. The researcher determined that there are other situations that are not suitable forparticipation.