A Phase 2 Study of EZN-2208 in Patients With Metastatic Breast Cancer

Inclusion Criteria: * Histologically confirmed breast adenocarcinoma that is metastatic. Receptor status of the tumor must be known. * Disease progression during or after immediate previous therapy, or intolerable toxicity leading to cessation of immediate previous therapy * Previous treatment for MBC: * AT Cohort: Prior AT required as adjuvant or metastatic therapy; no more than 2 prior chemotherapy regimens for MBC. * ATX Cohort: Prior ATX required as adjuvant or metastatic therapy;no more than 4 prior chemotherapy regimens for MBC. * For patients with positive receptor status: * Patients with HER2+ MBC must have received prior trastuzumab. * Patients with ER+ MBC must have received prior hormone therapy. * Measurable disease by RECIST Version 1.1 * Women 18 years or older * ECOG performance status of 0 to 2 * Adequate bone marrow, renal and hepatic functions Exclusion Criteria: * Major surgery within 3 weeks before study start * Known or suspected brain metastases requiring intervention with steroids and/or radiation therapy * Prior chemotherapy, immunotherapy, non-investigational agent, or other therapy used to treat the cancer within 3 weeks before scheduled administration of EZN-2208 * History of other primary cancer within 5 years of enrollment, unless 1. Curatively resected non-melanomatous skin cancer, or 2. Curatively resected cervical cancer * Lack of recovery to Grade 1 from any reversible side effects related to the administration of an investigational agent, chemotherapy, or other prior treatments for the cancer * Current participation in another clinical study with an investigational agent and/or use of an investigational drug (not including investigational use of an approved drug) in the 30 days before the first administration of EZN-2208 * Known chronic infectious disease, such as AIDS