A Study of Vantictumab (OMP-18R5) in Combination With Paclitaxel in Locally Recurrent or Metastatic Breast Cancer

Inclusion Criteria: * Signed Informed Consent Form * Age ≥18 years * Histologically documented adenocarcinoma of the breast with locally recurrent or metastatic disease o Patients with breast cancer overexpressing HER2 are not eligible. * Availability of tumor tissue, either archival FFPE or obtained at study entry through fresh biopsy * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * All acute treatment-related toxicity from prior therapy must have resolved to Grade ≤ 1 prior to study entry * Adequate hematologic and end-organ function * Evaluable or measurable disease per RECIST v1.1 * For women of childbearing potential, agreement to use two effective forms of contraception Exclusion Criteria: * Known significant dose delays during prior treatment with a taxane due to drug-related toxicities * Prior treatment with more than two regimens of systemic cytotoxic chemotherapy for locally recurrent or metastatic disease * Treatment with any anti-cancer therapy within 3 weeks prior to initiation of study treatment