A group of patients with confirmed breast cancer that has spread locally or to distant sites will receive an antibody‑drug conjugate called Trastuzumab Deruxtecan. Before starting this therapy, a small amount of a specially labeled antibody, identified as 89Zr‑Trastuzumab, will be given by injection to allow a picture of the tumor to be taken with a scanning technique.
The study’s purpose is to find out whether the picture obtained with the labeled antibody together with an early FDG PET/CT scan can predict how the cancer will respond to the antibody‑drug treatment after a few cycles. After the injection of the imaging agent, participants will have a scan using PET technology, then begin the standard course of the antibody‑drug. Additional scans will be performed after three treatment cycles and later in the follow‑up period to see how the disease is behaving.
Response will be checked by looking at changes in tumor activity on the PET images, called a metabolic response, and by measuring tumor size on standard pictures taken with CT or MRI, referred to as a radiological response. The study will also record how long patients go without the disease getting worse (progression‑free survival) and how long they live overall (overall survival). These measurements help researchers understand whether the early imaging can be a useful tool for guiding treatment decisions.
Belgium 
