• Age: ≥ 18 years

• Eastern Cooperative Oncology Group (ECOG) ≤ 1

• Life expectancy \> 3 months

• Histologically confirmed metastatic triple negative breast cancer. Triple negative status will be defined as estrogen receptor (ER) and progesterone receptor (PR) ≤ 10% and HER2 negative (by immunohistochemistry \[IHC\] or fluorescence in situ hybridization \[FISH\]), per American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines

• Patients must have progressed on 1-2 prior lines of systemic therapy (chemotherapy and/or drug-antibody conjugate) in the metastatic setting

• Measurable or evaluable disease by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions

• Fully recovered from the acute toxic effects (except alopecia) to ≤ grade 2 from prior anti-cancer therapy

• For Phase 2 expansion only, must be PD-L1 negative. Note: For Phase 1 safety cohort, any PD-L1 status will be allowed to enroll.

• Patients must have adequate organ function as defined in the following:

• Absolute neutrophil count (ANC) ≥ 1,500/mm\^3

• Platelets ≥ 100,000/mm\^3

• Hemoglobin ≥ 9.0 g/dL or ≥ 5.6 mmol/L. Criteria must be met without erythropoietin dependency and without packed red blood cell (pRBC) transfusion within last 2 weeks

• Total serum bilirubin ≤ 1.5 x upper limit of normal (ULN) OR direct bilirubin ≤ ULN for participants with total bilirubin levels \> 1.5 x ULN

• Aspartate aminotransferase (AST) ≤ 1.5 x ULN or ≤ 3 x ULN with liver metastases

• Alanine aminotransferase (ALT) ≤ 1.5 x ULN or ≤ 3 x ULN with liver metastases

• Creatinine ≤ 1.5 x ULN OR calculated creatinine clearance ≥ 30 mL/min for participant with creatinine levels \>1.5 x institutional ULN

• International normalized ratio (INR) or prothrombin time (PT), activated partial thromboplastin time (aPTT) ≤ 1.5 x ULN unless participant is receiving anticoagulant therapy as long as PT or aPTT is within therapeutic range of intended use of anticoagulants

• Left ventricular ejection fraction (LVEF) ≥ 50% by echocardiogram

• Women of childbearing potential (WOCBP): negative urine or serum pregnancy test

‣ If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required

• A male participant must agree to use a contraception during the treatment period and for at least 120 days after the last dose of study treatment and refrain from donating sperm during this period

• A female participant is eligible to participate if she is not pregnant, not breastfeeding, and at least one of the following conditions applies:

‣ Not a woman of childbearing potential (WOCBP) OR

⁃ Females of child-bearing potential must be willing to use effective contraception during study and for 120 days after the last dose

• Written informed consent obtained from subject and ability for subject to comply with the requirements of the study.