This study is being conducted to compare the efficacy and safety of tesetaxel administered once every 3 weeks in a 21-day cycle, tesetaxel administered once weekly for 3 consecutive weeks in a 28-day cycle, and capecitabine administered twice daily for 14 consecutive days in a 21-day cycle.

Key inclusion criteria:

1. Female
2. At least 18 years of age
3. Locally advanced non-resectable or metastatic breast cancer
4. HER2 negative disease
5. Measurable disease per revised RECIST, Version 1.1
6. Eastern Cooperative Oncology Group performance status 0 or 1
7. Chemotherapy naïve, OR 1 prior chemotherapy regimen in the neoadjuvant or adjuvant setting provided the patient has had a disease-free interval of ≥ 12 months after ending this chemotherapy. If the neoadjuvant or adjuvant chemotherapy included a taxane, ≥ 2 years must have passed since this treatment ended.
8. Documented disease recurrence or progression
9. Adequate bone marrow, hepatic, and renal function
10. Ability to swallow an oral solid-dosage form of medication
11. Written informed consent

Key exclusion criteria:

1. Known metastasis to the central nervous system
2. Other cancer within the preceding 5 years other than curatively treated basal or squamous cell carcinoma of the skin or carcinoma of the cervix in situ
3. Significant medical disease other than breast cancer
4. Presence of neuropathy > Grade 1 (NCI CTC)
5. History of hypersensitivity to a taxane or capecitabine, other fluoropyrimidine agents, or any of their ingredients
6. History of severe or unexpected reaction to fluoropyrimidine therapy
7. Need to continue any regularly-taken medication that is a potent inhibitor or inducer of the CYP3A pathway
8. Less than 2 weeks since use of a medication or ingestion of an agent, beverage, or food that is a potent inhibitor or inducer of the CYP3A pathway
9. Known dihydropyrimidine dehydrogenase deficiency
10. Pregnancy or lactation