HER2 PET

HER2 PET images HER2 across every metastasis at once using a radiolabelled HER2 binder, either 89Zr-trastuzumab or smaller 68Ga- and 18F-labelled affibodies and nanobodies such as 68Ga-ABY-025 and 18F-GE-226. The result is a whole-body receptor map rather than a single biopsy, which matters because HER2 expression varies between lesions. The ZEPHIR and IMPACT trials studied these tracers, and uptake was predictive of response to T-DM1. It is most useful in heterogeneous HER2-low disease, where one biopsy may be unrepresentative and HER2-directed ADCs now have indications. Studied since 2010, it is not yet approved; trials have been small, and full-antibody tracers need days between injection and imaging, which smaller binders aim to shorten. It shows how much HER2 each tumour deposit carries without a needle.