Study of AZD5863 in Adult Participants With Advanced or Metastatic Solid Tumors

Key Inclusion Criteria:

* Age ≥ 18 at the time of signing the informed consent
* Histologically confirmed diagnosis of adenocarcinoma of the stomach, gastro-esophageal junction, esophagus, or pancreas
* Must have at least one measurable lesion according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1
* Must show positive CLDN18.2 expression in tumor cells as determined by central immunohistochemistry (IHC)
* Eastern Cooperative Oncology Group Performance status (ECOG PS): 0-1 at screening
* Predicted life expectancy of ≥ 12 weeks
* Adequate organ and bone marrow function measured within 28 days prior to first dose as defined by the protocol
* Contraceptive use by men or women should be consistent with local regulations, as defined by the protocol
* Must have received at least one prior line of systemic therapy in the advanced/metastatic setting

Key Exclusion Criteria:

* Unresolved toxicity from prior anticancer therapy of Common Terminology Criteria for Adverse Events (CTCAE) Grade ≥ 2 except for those defined by the protocol
* Participant experienced unacceptable cytokine release syndrome (CRS) or Immune Effector Cell Associated Neurotoxicity (ICANS) following prior T cell engagers (TCE) or chimeric antigen receptor T (CAR-T) cell therapy
* Previous history of hemophagocytic lymphohistiocytosis (HLH) / macrophage activation syndrome (MAS)
* Active or prior documented autoimmune or inflammatory disorders within 3 years of start of treatment
* central nervous system (CNS) metastases or CNS pathology, as defined by the protocol, within 3 months prior to consent
* Infectious disease including active human immunodeficiency virus (HIV), active hepatitis B/C, uncontrolled infection with EBV, uncontrolled active systemic fungal, bacterial or other infection
* Cardiac conditions as defined by the protocol
* History of thromboembolic event within the past 3 months prior to the scheduled first dose of study intervention
* Participant requires chronic immunosuppressive therapy
* Participants on anticoagulation therapy with long-acting anticoagulants or other class of anticoagulants at therapeutic doses Module 3 - Active or ongoing interstitial lung disease / pneumonitis, serious chronic gastrointestinal conditions Module 3 - Any of the following cardiac conditions as determined by investigator: Complex ventricular arrhythmia, symptomatic heart failure, Cardiomyopathy, myocardial infarction or unstable angina (within past 6 months) and uncontrolled hypertension.

Module 3 - Known allergy or hypersensitivity to rilvegostomig or its excipients Module 3 - Prior exposure to an anti-TIGIT therapy