A Phase 2, Single-Arm, Open-Label Study of Trilaciclib Administered Prior to Sacituzumab Govitecan-hziy in Patients With Unresectable Locally Advanced or Metastatic Triple-Negative Breast Cancer Who Received at Least Two Prior Treatments, at Least One in the Metastatic Setting

• Adult ( ≥18 years of age), female or male participant with measurable (per RECIST v1.1), unresectable locally advanced or metastatic TNBC

• Documentation of histologically or cytologically confirmed ER-negative, PR-negative, and HER2-negative tumor per the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (ASCO/CAP) criteria.

• Measurable disease as defined by RECIST v1.1.

• Considered to be eligible to receive sacituzumab govitecan-hziy treatment, in the Investigator's judgment.

• Participants must have received 2 or more prior lines of systemic therapy, at least one of them in the metastatic setting.

• Radiation therapy for metastatic disease is permitted as long as the participant has at least 1 measurable lesion that has not been irradiated. Participants should be sufficiently recovered from the effects of radiation as determined by the Investigator but must have completed radiotherapy at least 2 weeks prior to enrollment.

• ECOG performance status of 0 or 1.

• Adequate organ function as demonstrated by the following laboratory values:

‣ Hemoglobin ≥9.0 g/dL

⁃ Absolute neutrophil count (ANC) ≥1.5 × 10\^9/L;

⁃ Platelet count ≥100 × 10\^9/L;

⁃ Estimated glomerular filtration rate ≥30 mL/minute/1.73 m\^2;

⁃ Total bilirubin ≤1.5 × upper limit of normal (ULN);

⁃ ALT and AST ≤3 × ULN in the absence of liver metastasis or ≤5 × ULN in the presence of liver metastasis.

• Resolution of nonhematologic toxicities from prior systemic therapy, radiation therapy, or surgical procedures to Common Terminology Criteria for Adverse Events (CTCAE) ≤ Grade 1 (except alopecia or peripheral neuropathy that may be Grade 2 or less).

⁃ Predicted life expectancy of ≥3 months.

⁃ Contraceptive use by men or women should be consistent with local guidelines regarding the methods of contraception for those participating in clinical studies.

⁃ Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form and in this protocol.