The primary purpose of this study is to evaluate the clinical safety profile, tolerability, and pharmacokinetic (PK) characteristics of RAD140 in hormone receptor positive breast cancer.

This is a first in humans study that is designed to evaluate the clinical safety profile, tolerability, and pharmacokinetic (PK) characteristics of RAD140 in hormone receptor positive breast cancer.

Key Inclusion Criteria:

• Progressive metastatic or locally advanced or metastatic breast cancer.
• Clinically confirmed as postmenopausal.
• Eastern Cooperative Oncology Group (ECOG) score of 0 to 1 at screening.

Key Exclusion Criteria:

• HER2 positive patients by local laboratory testing.
• Triple negative breast cancer.
• Any chemotherapy within the 28 days prior to the first dose of study drug.
• Any non-chemotherapy anti-cancer drug less than 5 half-lives (30 days for biologics) or less than 14 days for small molecule therapeutics, or if half-life is not known.
• Tamoxifen and aromatase inhibitors within 14 days prior to the first dose of study drug.
• Fulvestrant within 30 days prior to first dose of study drug.
• Any investigational drug therapy within 5 half-lives of the previous investigational study drug or 30 days, whichever is shorter.
• Radiation therapy for breast cancer within 2 weeks of dosing and planning to have radiation therapy during participation in this study.
• Known history of human immunodeficiency virus infection (HIV) or hepatitis C or active hepatitis B infection, unless the patient was diagnosed >10 years prior to enrollment and no evidence of active liver disease.
• Currently taking testosterone, methyltestosterone, oxandrolone (Oxandrin), oxymetholone, danazol, fluoxymesterone (Halotestin), or testosterone-like agents.
• Untreated or uncontrolled brain metastasis.
• Diagnosed with or treated for cancer within the previous 2 years, other than breast cancer or non-melanoma carcinoma of the skin.
• Pregnant and nursing females.