Molecular Imaging of HER2 Expression in Breast Cancer Using 99mTc-HE3-G3

Inclusion Criteria: 1. Subject is \> 18 years of age 2. Diagnosis of primary breast cancer with possible lymph node metastases 3. Availability of results from HER2 status previously determined on material from the primary tumor, either 1. HER2-positive, defined as a immunohistochemical test score of 3+ or FISH positive or 2. HER2-negative, defined as a immunohistochemical test score of 0 or 1+; or else if 2+ then FISH negative 4. Volumetrically quantifiable tumour lesions on CT or MRI, with at least one lesion \> 1.0 cm in greatest diameter outside of the liver and kidneys 5. Hematological, liver and renal function test results within the following limits: * White blood cell count: \> 2.0 x 10\^9/L * Haemoglobin: \> 80 g/L * Platelets: \> 50.0 x 10\^9/L * Bilirubin =\< 2.0 times Upper Limit of Normal * Serum creatinine: Within Normal Limits 6. A negative pregnancy test (serum beta-human chorionic gonadotropin, beta-HCG) at screening for all patients of childbearing potential. Sexually active women of childbearing potential participating in the study must use a medically acceptable form of contraception for at least 30 days after study termination 7. Subject is capable to undergo the diagnostic investigations to be performed in the study 8. Informed consent Exclusion Criteria: 1. Second, non-breast malignancy 2. Active current autoimmune disease or history of autoimmune disease 3. Active infection or history of severe infection within the previous 3 months (if clinically relevant at screening) 4. Known HIV positive or chronically active hepatitis B or C 5. Administration of other investigational medicinal product within 30 days of screening 6. Ongoing toxicity \> grade 2 from previous standard or investigational therapies, according to US National Cancer Institute's