Inclusion Criteria:

- Biopsy-proven breast cancer, metastatic (persistent or recurrent).

- Failed ≥1 line of therapy (endocrine or chemotherapy) for metastatic disease.

- Min. 3 distinct metastatic sites, at least one measurable lesion which is at least 1
cm or larger in largest diameter.

- Must be ≥4 weeks since all of the following treatments (recovered from toxicity of
prior treatment to ≤Grade 1, excluding alopecia):

- major surgery;

- radiotherapy;

- chemotherapy (≥6 weeks since therapy if a nitrosourea, mitomycin, or monoclonal
antibodies such as bevacizumab);

- immunotherapy;

- biotherapy/targeted therapies.

- >18 years of age.

- Life expectancy >6 months.

- Eastern Cooperative Oncology Group (ECOG) status 0 or 1.

- Adequate organ function including:

- Hemoglobin ≥10.0g/dL, absolute neutrophil count (ANC) ≥1,500/mm3, and platelets
≥100,000/mm3.

- Hepatic: Serum total bilirubin ≤1.5x upper limit of normal (ULN) (Patients with
Gilbert's Disease may be included if total bilirubin is ≤3.0mg/dL), alanine
aminotransferase (ALT), and aspartate aminotransferase (AST) ≤2.5xULN. If
patient has known liver metastases, ALT and/or AST ≤5xULN are allowed.

- Renal: creatinine clearance ≥60mL/min.

- Prothrombin (PT) and partial thromboplastin times (PTT)
- Negative for hepatitis viruses B and C unless consistent with prior vaccination or
prior infection with full recovery.

- Patients of childbearing potential must agree to use effective contraception while on
study, and for ≥3 months after last treatment.

- Understand and sign written informed consent document. No consent by durable power of
attorney.

Exclusion Criteria:

- Second malignancy - unless following curative intent therapy, has been disease free
for ≥2 years with probability of recurrence <5%. Curatively treated early-stage
squamous cell carcinoma of the skin, basal cell carcinoma of the skin, or cervical
intraepithelial neoplasia (CIN) are allowed.

- Concurrent cancer therapy.

- Uncontrolled central nervous system (CNS) metastases, meningeal carcinomatosis,
malignant seizures, or disease that causes or threatens neurologic compromise (e.g.
unstable vertebral metastases).

- History of ascites or pleural effusions, unless successfully treated.

- Organ transplant, including allogeneic bone marrow transplant.

- Immunosuppressive therapy including:

- Systemic corticosteroid therapy, including replacement therapy for
hypoadrenalism. Inhaled or topical corticosteroids are allowed (if therapy is <5
days and is limited to systemic steroids as antiemetics);

- Cyclosporine A, tacrolimus, or sirolimus.

- Investigational agents within 4 weeks prior to study enrollment (≥6 weeks if
treatment was long-acting agent such as monoclonal antibody).

- Significant or uncontrolled medical illness, e.g. congestive heart failure (CHF),
myocardial infarction, symptomatic coronary artery disease, significant ventricular
arrhythmias within the last 6 months, or significant pulmonary dysfunction. Patients
with remote history of asthma or active mild asthma may participate.

- Active infection, including unexplained fever (>38.5°C).

- Systemic autoimmune disease (e.g. systemic lupus erythematosus, active rheumatoid
arthritis).

- Known allergy to any component of GC1008.

- Active thrombophlebitis, thromboembolism, hypercoagulability states, bleeding, or
anti-coagulation therapy (including anti platelet agents i.e. aspirin, clopidogrel,
ticlopidine, dipyridamole, other agents inducing long-acting platelet dysfunction).
Patients with history of deep venous thrombosis are allowed if treated, completely
resolved, and no treatment for >4months.

- Calcium >11.0mg/dL (2.75mmol/L) unresponsive or uncontrolled in response to standard
therapy (e.g. bisphosphonates).

- Patients who, in the opinion of the Investigator, have significant medical or
psychosocial problems, including, but not limited to:

- Other serious non-malignancy-associated conditions that may be expected to limit
life expectancy or significantly increase the risk of SAEs;

- Conditions, psychiatric, substance abuse, or other, that, in the opinion of the
Investigator, would preclude informed consent, consistent follow-up, or
compliance with any aspect of the study;

- Pregnant or nursing women.