A Study of CDX-011 (CR011-vcMMAE) in Patients With Advanced GPNMB-expressing Breast Cancer

CDX-011 consists of an antibody attached to a drug, monomethyl auristatin E (MMAE), that can
kill cancer cells. The antibody delivers the drug to cancer cells by attaching to a protein
called glycoprotein NMB (GPNMB) that is expressed on the cancer cell. The MMAE is then
released inside of the cell, where it interferes with cell growth and may lead to cell
death.

This study will examine the effectiveness and safety of CDX-011 in patients with advanced
breast cancer that makes the GPNMB protein. To better assess this, the effect of CDX-011
will be compared to treatment with currently available cancer chemotherapy.

Eligible patients who enroll in the study will be randomly assigned by chance to receive
treatment with CDX-011 or with a chemotherapy chosen by their study doctor from a list of
currently available drugs ("Investigator's Choice" chemotherapy). For each three patients
enrolled, two will receive CDX-011 and one will receive treatment with "Investigator's
Choice". Patients initially assigned to "Investigator's Choice" chemotherapy may be offered
treatment with CDX-011 if their cancer worsens during this initial treatment.

All patients enrolled in the study will be closely monitored to determine if their cancer is
responding to treatment, and for any side effects that may occur.

Inclusion Criteria:

Among other criteria, patients must meet all of the following conditions to be eligible
for the study:

1. 18 years of age or older.

2. Locally advanced or metastatic breast cancer.

3. Previous treatment with at least two but no more than seven prior chemotherapy
treatments for progressive, recurrent or metastatic breast cancer.

4. Unless not a candidate for these agents, prior therapies must have included a taxane,
an anthracycline, and capecitabine, as well as trastuzumab and lapatinib for patients
whose tumors are positive for the human epidermal growth factor receptor 2 (HER2).
(Patients who received incomplete courses of therapy with these agents due to
intolerance will be eligible.)

5. Breast cancer tumor confirmed to express GPNMB. This will be determined by submitting
a tissue sample (obtained during a diagnostic biopsy or surgery) to a central
laboratory for analysis.

Exclusion Criteria:

Among other criteria, patients who meet any of the following conditions are NOT eligible
for the study:

1. Ongoing neuropathy or other chemotherapy or radiation-related toxicities that are
moderate (Grade 2) or worse in severity.

2. Known brain metastases, unless previously treated and asymptomatic for 2 months and
not progressive in size or number for 2 months.

3. Significant cardiovascular disease or any other underlying medical condition that, in
the Investigator's opinion, will make the administration of study treatment (CDX-011
or chemotherapy) hazardous or would obscure the interpretation of side effects.