Phase Ib/II Study of PLX 3397 and Eribulin in Patients With Metastatic Breast Cancer

Inclusion Criteria: * Pathologically confirmed diagnosis of breast cancer with documented progressive disease. * Patients with stable brain metastases are eligible for this trial. * At least one prior chemotherapy regimen for metastatic breast cancer. Prior treatment must be discontinued at least 2 weeks before treatment start. * Concomitant therapy with bisphosphonates is allowed. * Stable dose coumadin anticoagulation is allowed, providing that anticoagulation can be safely held to an International Normalized Ratio (INR) within normal range for the purpose of tumor biopsy. Low molecular weight heparin (LMWH is the preferred method of anticoagulation. * Prothrombin time (PT)/International Normalized Ratio (INR) and partial thromboplastin time (PTT) within institutional normal limits within two weeks before initial biopsy. * Measurable disease, as defined by RECIST guidelines or evaluable disease. Bone metastases must be evaluable. * Disease amenable to core biopsy. Patients with pulmonary metastases as their only site of disease may enroll on this trial and will not undergo biopsy. * For Phase I: patients with human epidermal growth factor receptor 2 (HER2) overexpressing disease must have been previously treated with trastuzumab. Patients with HER2 overexpressing disease are not eligible for the Phase II trial. * Age eighteen years or older. * Eastern Cooperative Oncology Group (ECOG) performance status \</= 2. * Life expectancy of \>/= 12 weeks. * Patients with \< grade 1…