Description:

The goal of this clinical trial is to test a new PET tracer in patients with HER2-positive breast or gastric cancer. This tracer is made of radioactively labeled trastuzumab, and can show where HER2 is present in the body using a PET-scan. For this research, the investigators make PET-scans in people with HER2-positive, metastasized breast- or gastric cancer. The investigators will investigate if the new HER2-tracer correctly shows all tumor lesions. In the future, this method may be useful to help predict who will benefit from certain HER2-directed therapies.