Pilot Imaging Study With 89Zr-Trastuzumab in HER2-positive Metastatic Breast Cancer Patients

Inclusion criteria: 1. All patients selected for this imaging study are patients scheduled to start trastuzumab-based therapy for advanced HER2 positive breast cancer (This includes trastuzumab alone, trastuzumab + chemotherapy, trastuzumab + endocrine therapy). 2. Histologically confirmed HER 2 positive (defined as FISH amplification ratio more than 2.2) invasive carcinoma of the breast (primary tumor at diagnosis) with locally recurrent or metastatic disease. 3. Patients with FDG-PET positive metastatic lesions. 4. Brain metastases are allowed provided they are controlled and they are not the sole site of metastatic disease. 5. Patient planned to have metastatic site biopsy for HER2 status control. 6. Age ≥ 18 years 7. Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0 to 1 8. For women of childbearing potential a pregnancy test will be done and an agreement to use a highly-effective non hormonal form of contraception. 9. Agreement from the patient to participate in this imaging study and if indicated agreement to biopsy one or two accessible lesions. 10. Signed written informed consent (approved by the Ethics Committee) obtained prior to any study procedure Exclusion criteria: 1. Current severe, uncontrolled systemic disease (e.g., clinically significant cardiovascular, pulmonary, or metabolic disease) 2. Pregnant or lactating women 3. Current known infection with HIV, HBV, or HCV 4. Known severe hypersensitivity to trastuzumab 5. Assessed by the investigator to be unable or unwilling to comply with the requirements of the protocol 6. Patients with bone only metastases are not eligible 7. Psychiatric illness/social situations that would limit compliance with study requirements 8. Patients who received lapatinib within the 7 days prior to HER immunoPET/CT.