Study of AMG 910 in Subjects With CLDN18.2-Positive Gastric and Gastroesophageal Junction Adenocarcinoma

Inclusion Criteria: * Subjects with histologically or cytologically confirmed metastatic or locally advanced unresectable gastric or GEJ adenocarcinoma positive for CLDN18.2. * Subjects should not be eligible for curative surgery and should have been refractory to or have relapsed after two or more prior lines of standard systemic therapy that included a platinum, a fluoropyrimidine, either a taxane or irinotecan, and an approved vascular endothelial growth factor receptor (VEGFR) antibody/tyrosine kinase inhibitor (TKI) and depending on country-specific standards and approvals. * For subjects eligible for human epidermal growth factor receptor 2 (HER2) directed therapy, prior systemic therapy should have included a HER2 targeting antibody approved for treatment of gastric cancer. * Subjects may also be included if the aforementioned therapeutic options were medically not appropriate for them. In these cases, the reason(s) why required prior therapies for gastric cancer were medically not appropriate should be documented in the subject's electronic case report form (eCRF). * For dose-expansion only: Subjects with at least 1 measurable lesion greater than or equal to 10mm which has not undergone biopsy within 3 months of screening scan. This lesion cannot be biopsied at any time during the study. * Subjects with stable condition and anti-coagulative therapy ongoing for at least 1 month, no obvious signs and symptoms of bleeding, and coagulation parameters are fulfilled. * Sub…