Intra-patient HER2 heterogeneity expression in breast cancer [27] has spurred interest in [89Zr]trastuzumab PET/CT for whole-body HER2 assessment, aiding treatments like HER2-targeting trastuzumab emtansine (T-DM1), which targets tumour HER2 status. The gene discussed is ERBB2; the disease is breast cancer.