AZD0901 Compared With Investigator's Choice of Therapy in Participants With Second- or Later-line Advanced or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma Expressing Claudin18.2

Exclusion criteria

• . Participants with known HER2 positive status as defined as IHC 3+ or IHC 2+/ISH + (Cases with HER2: CEP17 ratio ≥ 2 or an average HER2 copy number ≥ 6.0 signals/cell are considered positive by ISH). Participants must undergo local (or have had) HER2 testing by IHC/ISH, and the most recent result of HER2 status will be used to determine the eligibility.
• . Participant has significant or unstable gastric bleeding and/or untreated gastric ulcers.
• . CNS metastases or CNS pathology including: epilepsy, seizures or aphasia within 3 months prior to consent, severe brain injury, dementia, Parkinson's disease, neurodegenerative diseases, cerebellar disease, severe uncontrolled mental illness, psychosis, CNS involvement of autoimmune diseases.
• . Participant has known clinically significant corneal disease (eg, active keratitis or corneal ulcerations).
• . Persistent toxicities (CTCAE Grade ≥ 2) caused by previous anticancer therapy, excluding alopecia. Participants with irreversible toxicity that is not reasonably expected to be exacerbated by study intervention may be included (eg, hearing loss).
• . Prior exposure to any ADC with MMAE payload or any CLDN18.2 targeting treatment other than naked monoclonal antibody (eg, CLDN18.2 targeting CAR-T cell therapy, multi-specific antibody including targeting CLDN18.2, etc).
• . History of thromboembolic events:
• . Participants with venous thromboembolism within the past 6 months prior to randomization: participants with venous port or catheter thrombosis or superficial venous thrombus that do not require treatment or are stable on treatment with anticoagulants are excepted