Inclusion Criteria:  Age 18 years and older  Active cancer of the type adenocarcinoma (of the esophagus, of the stomach, of the bile ducts, or of the pancreas) documented by a CT scan performed within the last 8 weeks at the time of recruitment.  An active cancer is defined as at least one lesion identified as stable or progressive neoplastic on CT imaging. A lesion treated with local therapy (e.g., external radiotherapy, cryoablation, radiofrequency ablation, resection) is not counted for inclusion criteria if this is done between the CT scan and the 68Ga-PSMA PET imaging. A lesion treated prior to the last CT scan may be considered eligible if progression is documented at the last CT scan. Able to provide free and informed consent. Feasibility to perform 68Ga-PSMA PET within 2 months of the CT scan that was used for inclusion.  Exclusion Criteria:  Other active cancer (non-metastatic non-melanoma skin cancer excluded). Cancer in remission for at least 3 years will not be considered active. ECOG > 3. Pregnant woman. Unable to follow study rules.