Inclusion Criteria:

- Locally advanced/unresectable or metastatic breast cancer

- Eighteen years of age or above

- Able to understand and sign an informed consent (or have a legal representative who
is able to do so)

- Measurable disease according to RECIST v1.1

- ECOG Performance Score of 0 or 1

- Adequate bone marrow, hepatic, renal and cardiac function

- Willing to abstain from sexual intercourse or to use an effective form of
contraception during the study and for 90 days following the last dose of MM-302

Exclusion Criteria:

- Patients for whom potentially curative anticancer therapy is available

- Active infection or fever > 38.5°C during screening visits or on the first scheduled
day of dosing

- Symptomatic CNS disease

- Known hypersensitivity to any of the components of MM-302 or who have had
hypersensitivity reactions to fully human monoclonal antibodies

- Received other recent antitumor therapy

- Pregnant or breast feeding

- Patients with any other medical or psychological condition, deemed by the
Investigator to be likely to interfere with a patient's ability to sign informed
consent, cooperate and participate in the study, or interfere with the interpretation
of the results