Inclusion Criteria:

• Histologically proven adenocarcinoma of the stomach or the esophagogastric junction (Siewert type III), by gastroscopy;
• Age greater than or equal to 18 years;
• Surgically resectable, advanced tumor (cT3-4b, N0-3, M0), as determined on gastroscopy and a contrast-enhanced CT of thorax and abdomen. Intention to perform a gastrectomy, based on a multidisciplinary team meeting and shared decision making;
• Patients must have given written informed consent;
• Patients who have recently participated in an interventional study with an investigational medicinal product (IMP) may only participate if an interaction with study procedures is deemed unlikely by the study team (e.g. based on mechanism or washout period).

Exclusion Criteria:

• Siewert type I-II esophagogastric junction tumor;
• Unfit or unwilling to undergo study procedures;
• Unfit or unwilling to undergo surgery;
• Pregnancy at time of the [18F]AlF-FAPI-74 PET/CT scan, due to the investigational PET radiation burden;
• Incapacitated subjects without decision-making capacity;
• Medical or psychiatric conditions that compromise the patient's ability to give informed consent;
• Illiterate patients unable to complete the resource use and quality of life questionnaires;
• Inability to undergo PET/CT scans due to factors such as claustrophobia, weight limits, or the inability to lie flat for the duration of the scan (approximately 30 minutes).