Study of Cirmtuzumab and Paclitaxel for Metastatic or Locally Advanced, Unresectable Breast Cancer

* This is a phase 1b, open-label, non-randomized, fixed dose study in patients with HER2 negative metastatic, or locally advanced, unresectable breast cancer. * Cirmtuzumab and paclitaxel will be administered until disease progression or unacceptable toxicity. Cirmtuzumab or paclitaxel may be continued alone if the other drug is discontinued due to toxicity, as long as the subject is tolerating the drug and does not exhibit disease progression. * Blood and tissue samples will be collected at pre-specified times to enable pharmacokinetic and correlative studies. * Adverse events (AE) will be monitored throughout the trial. Reporting of AEs will be in accordance with CTCAE version 4.03. * Assessment of tumor response will be performed by physical examination and/or by radiographic imaging and according to the Response Evaluation Criteria in Solid Tumors (RECIST) v.1.1. * Patients will be assessed at 28 days following the last dose of cirmtuzumab to assess tumor response and at 56 days following the last dose of cirmtuzumab to assess any adverse events and to document any concomitant cancer therapy.