A Study of ZN-c5 in Participants With Breast Cancer

Inclusion criteria

• Signed and dated ICF
• Age ≥ 18 years of age, either gender
• Females must be postmenopausal as defined by at least one of the following:

• Age ≥ 60 years;
• Age < 60 years and cessation of regular menses for at least 12 consecutive months with no alternative pathological or physiological cause; and serum estradiol and follicle stimulating hormone levels within the local laboratory's normal reference range for postmenopausal females;
• Documented bilateral oophorectomy
• Histologically or cytologically confirmed diagnosis of adenocarcinoma of the breast
• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
• Adequate organ function defined as follows:

• Hematologic: Platelets ≥ 100 × 109/L; Hemoglobin ≥ 9.0 g/dL; Absolute neutrophil count ≥ 1.5 × 109/L (without platelet transfusion or any hematopoietic growth factors within previous 7 days of the hematologic laboratory values obtained at the Screening Visit)
• Hepatic: Aspartate aminotransferase (AST) / Alanine aminotransferase (ALT)

≤ 2.5 × upper limit of normal (ULN); Total or conjugated bilirubin ≤ 1.5 × ULN

• Renal: Serum creatinine ≤ 1.5 × ULN or creatinine clearance (CrCl) ≥ 60 mL/min

Exclusion criteria

• Major surgery, defined as any surgical procedure that involves general anesthesia and a significant incision (i.e., larger than what is required for placement of central venous access, percutaneous feeding tube, or biopsy) within 28 days of the first administration of study drug
• Treatment with another investigational drug or other intervention within 28 days before the first administration of study drug
• Impairment of gastrointestinal (GI) function or GI disease that may significantly alter the absorption of oral medication, including any unresolved nausea, vomiting, or diarrhea that is CTCAE v.5.0 Grade > 1
• Myocardial infarction, symptomatic congestive heart failure (New York Heart Association Classification > Class II), unstable angina, or serious uncontrolled cardiac arrhythmia within the last 6 months of study Day 1
• Uncontrolled inter-current illness
• History or evidence of clinically significant disorder, condition, or disease that, in the opinion of the Investigator would pose a risk to subject safety or interfere with the study evaluations, procedures, or completion