The intravenously administered taxane, paclitaxel, is one of the most commonly employed agents for the treatment of both localized and advanced breast cancer.

Tesetaxel is an orally administered taxane that is in development as first- and second-line treatment for patients with advanced cancers. This study is being undertaken to determine the efficacy and safety of tesetaxel administered as first-line therapy to patients with metastatic breast cancer.

Primary Inclusion Criteria:

• Female
• At least 18 years of age
• Histologically or cytologically confirmed adenocarcinoma of the breast
• Stage IV disease
• HER2 status negative
• Measurable disease (revised RECIST; Version 1.1)
• Eastern Cooperative Oncology Group performance status 0 or 1
• Life expectancy of at least 3 months
• Chemotherapy naïve or 1 prior chemotherapy regimen in the adjuvant setting (Prior taxane-based adjuvant therapy allowed provided patient had a disease-free interval of at least 12 months after completing this adjuvant therapy)
• Prior hormonal therapy, aromatase inhibitor therapy, and immunotherapy allowed
• Prior radiotherapy in the adjuvant setting allowed provided that less than 25% of the bone marrow had been irradiated
• Adequate bone marrow, hepatic, and renal function, as specified in the protocol
• At least 4 weeks and recovery from effects of prior surgery, hormonal therapy, aromatase inhibitor therapy, immunotherapy, radiotherapy, or other therapy with an approved or investigational agent
• Ability to swallow an oral solid-dosage form of medication

Primary Exclusion Criteria:

• Known metastasis to the central nervous system
• History of other malignancy within the last 5 years other than curatively treated basal and squamous cell carcinoma of the skin or carcinoma of the cervix in situ
• Significant medical disease other than Stage IV breast cancer
• Presence of neuropathy > Grade 1 (NCI CTC, Version 4.0)
• History of hypersensitivity to a taxane
• Need to continue any regularly-taken medication that is a potent inhibitor or inducer of the CYP3A pathway or P-glycoprotein activity