[89Zr]trastuzumab for PET imaging of HER2-positive lesions in patients with metastatic breast cancer

To investigate the use of [89Zr]trastuzumab for high-resolution, quantitative and sensitive HER2 PET imaging. A feasibility study was performed to determine optimal conditions of [89Zr]trastu-zumab dosage and timing of scans for visualization and quantification of HER2-positive lesions. DESIGN AND METHODS HER2-positive metastatic breast cancer patients received 37 MBq [89Zr]trastuzumab at three doses of trastuzumab: 10 or 50 mg when trastuzumab-naive and 10 mg trastuzumab while on trastuzumab treatment. Patients underwent ≥ PET scans around day 2 and 5 after [89Zr] trastuzumab injection. RESULTS 14 patients were included. The optimal moment to assess [89Zr]-trastuzumab tumour uptake was 4-5 days after tracer injection. Trastuzumab-naive patients required 50 mg [89Zr] trastuzumab and for patients on trastuzumab treatment 10 mg was adequate. [ 89Zr]trastuzumab PET imaging detected not only most of the known tumour lesions in liver, lung, bone and brain, but also unknown brain and bone lesions. The relative uptake values (mean ± SD) in liver, bone and brain lesions were 12.8 ± 5.8, 4.1 ± 1.6 and 3.5 ± 4.2, respectively, while relative uptake values in normal liver, spleen, kidneys and brain were 5.9 ± 4.2,2.8 ± 0.7, 4.0 ± 0.7 and 0.20 ± 0.1, respectively. CONCLUSION PET imaging of HER2 with [89Zr] trastuzumab can identify HER2-positive lesions in patients with HER2-positive metastatic breast cancer, when an appropriate antibody dose is used. In addition it allows quantification of [89Zr]trastuzumab uptake in these lesions.