In this study, conducted by Gebhart et al., including 56 HER2+ metastatic BC patients, baseline 89Zr-trastuzumab PET/CT indicated that patients with 89Zr-trastuzumab uptake were associated with longer trastuzumab emtansine treatment duration, compared to those with no uptake (11.2 versus 3.5 months) and allowed to select patients who will benefit from HER2-targeting antibody–drug conjugate trastuzumab emtansine [84]. The gene discussed is ERBB2; the disease is breast cancer.