Inclusion Criteria:

1. Metastatic or locally recurrent adenocarcinoma of the breast (local recurrence not
amenable to surgical resection of curative intent)

2. Tumour HER2 positive by immunohistochemistry for HER2 protein over-expression or by
Fluorescence in situ Hybridization (FISH) for HER2 gene amplification, as defined by
American Society of Clinical Oncology/College of American Pathologists guidelines

3. Initiating treatment with TmAb

4. Clinically measurable disease by RECIST

Exclusion Criteria:

1. Less than 18 years of age.

2. Life expectancy < 12 weeks.

3. Only site of metastases is liver.

4. Eastern Cooperative Oncology Group (ECOG) performance status of > 2.

5. Currently receiving PmAb or lapatinib for treatment of MBC.

6. Having received TmAb as adjuvant therapy within the previous 12 months.

7. Required to receive another radiopharmaceutical during the first week of the study.

8. Hypersensitivity to monoclonal antibodies.

9. Left Ventricular Ejection Fraction (LVEF) < 50% at baseline (within 42 days of study
registration) as determined by either echocardiogram (ECHO) or Multi-Gated
Acquisition (MUGA) scan.

10. Hematology and/or biochemistry parameters outside acceptable ranges:

- absolute neutrophil count <1,500 cells/mm3,

- platelet count <100,000 cells/mm3,

- hemoglobin <9 g/dL,

- total bilirubin > upper limit of normal (ULN) (unless subject has documented
Gilbert's Syndrome),

- aspartate aminotransferase (AST) [serum glutamic oxaloacetic transaminase(SGOT)]
and alanine aminotransferase (ALT) [serum glutamic pyruvate transaminase(SGPT)]
>2.5 × ULN,

- serum creatinine >2.0 mg/dL or 177 μmol/L,

- alanine aminotransferase (ALP) >2.5 x ULN.

11. Known pregnancy or lactating female (e.g. positive serum beta-human chorionic
gonadotropin (B-hCG) pregnancy test).

12. For women of childbearing potential, failure to agree to use a highly effective form
of contraception (patient and/or partner, e.g., surgical sterilization) or two
effective forms of contraception (a reliable barrier method in conjunction with
spermicidal jelly, birth control pills, or contraceptive hormone implants) and to
continue its use for the duration of study treatment.

13. Any condition, which in the investigator's opinion would not make the patient a
suitable candidate for inclusion in the trial.

14. Participation in another clinical trial.

15. Inability to provide informed consent.