A Safety and Immunology Study of a Modified Vaccinia Vaccine for HER-2(+) Metastatic Breast Cancer

Inclusion Criteria: * Signed Informed Consent * Women, ≥ 18 years of age * Histologically documented, HER-2 (+) breast cancer with metastatic disease. * Evaluable or measurable disease. PATIENTS MAY BE NED. Patients must be assessed as having stable disease or better at the end of 1st- or 2nd-line chemotherapy. In addition, patients must have a tumor assessment within 28 days of the first planned dose of MVA-BN®-HER2, and have a response status of SD or better. * Prior chemotherapy for metastatic breast cancer * Completed 1st- or 2nd-line chemo for mBrCA at least 3 weeks (from the date of the last dose) prior to the first dose of MVA-BN®-HER2 * ECOG Performance Score of 0, 1, or 2 * Life expectancy ≥ 6 months * Left ventricular ejection fraction (LVEF) by ECHO or MUGA ≥ LLN * Women of childbearing potential must have a negative serum or urine pregnancy test, and must agree to use a medically acceptable barrier and/or chemical method of contraception throughout the study treatment period and for 28 days after the last dose of MVA-BN®-HER2 * No significant cardiac, bone marrow dysfunction, or coagulopathy. No significant hepatic or renal dysfunction. * A negative virology screen for HIV, hepatitis B surface antigen, hepatitis C, and HTLV-1 Exclusion Criteria: Patients may not have: * Known history of metastasis to the central nervous system * Congestive heart failure (NYHA Class III or IV), unstable angina, or cardiovascular disease such as stroke or myocardial infarction (current or within the past 6 months) * History of prior malignancies other than breast cancer within the past 5 years, excluding basal or squamous cell carcinoma of the skin or carcinoma in situ of the cervix * Known allergy to eggs, egg products, or aminoglycoside antibiotics, e.g., gentamicin or tobramycin * Chronic administration (5 or more consecutive days) of systemic corticosteroids within 14 days of the first planned dose of MVA-BN®-HER2. * History of or active autoimmune disease. Persons with vitiligo or thyroid disease taking thyroid replacement hormones are not excluded. * Prior solid organ or hematopoietic allogenic transplant(s) * Prior use of hematopoietic growth factors (e.g., GM-CSF) within 28 days of the first planned dose of MVA-BN®-HER2 * Receipt of an investigational agent within 28 days of the first planned dose of MVA-BN®-HER2 * Prior "vaccine" therapy for breast cancer at any time * Vaccination: Vaccinations with a live (attenuated) vaccine within 28 days of the first or last dose of study drug; or vaccinations with a killed (inactivated) vaccine within 14 days of the first or last dose of study drug. * A maximum cumulative dose of prior doxorubicin \> 360 mg/m2 or epirubicin \> 720 mg/m2 * Radiation therapy within 28 days of the first planned dose of MVA-BN®-HER2 or plans for radiation therapy after enrollment. * Pregnant, lactating, or nursing * Any condition which, in the opinion of the investigator, would prevent full participation in this trial or the long-term follow-up study, or would interfere with the evaluation of the trial endpoints