The study is designed as an open-label, randomized, parallel, two arm, multicenter, international Phase 3 study in patients with recurrent or metastatic breast cancer previously treated with cytotoxic chemotherapy regimens.

The primary study objective is to compare overall survival of patients who receive NKTR-102 given once every 21 days to patients who receive treatment of Physician's Choice selected from a list of seven single-agent intravenous therapies.