The goal of this phase II interventional clinical trial is to evaluate the HER2-status in tumor lesions measured by Gallium-68-ABY-025-uptake on PET/CT with HER2-status defined by reference standard (laboratory analyses) in patients with gastroesophageal cancer (GEAC) and metastatic breast cancer with low HER2 expression (HER2-low mBC).~The participants in GEAC cohort of the study will undergo two sessions of HER2 PET and one 18-Fluorodeoxyglucose (18F-FDG) PET/CT for study purposes. The first HER2 PET is performed within 21 days before initiation of the systemic oncological treatment and is followed by tumor biopsies. A second HER2 PET and a second 18F-FDG PET will be performed adjacent to response evaluation after 3 courses of oncological therapy. Data from the PET investigations will be compared to HER2 expression analyses of the biopsy specimen and correlated to disease and survival data at follow up one year after inclusion. Within the pilot study, participants with HER2 low mBC will undergo one HER2 PET followed by biopsies.
The goal of this phase II clinical trial is to improve the selection of patients with solid tumors who would benefit from effective treatment with HER2 targeted drugs. This will be achieved by examining patients with HER2 positive tumors in the esophagus or stomach or patients with advanced breast cancer with low HER2 expression (HER2low) with the HER2 specific positron emission tomography (PET) tracer ABY-025 (HER2-PET) and compare the imaging results with HER2 expression in tumor tissue derived from biopsies (reference standard).