Trilaciclib, a CDK 4/6 Inhibitor, in Patients Receiving Gemcitabine and Carboplatin for Metastatic Triple-Negative Breast Cancer (TNBC)

Inclusion Criteria:

1. Age >/= 18 years of age with evaluable locally advanced unresectable or metastaticTNBC.

2. Documentation of triple negative breast cancer (estrogen and progesterone receptor <1% and HER2-negative)

3. Prior systemic therapies (Cohort 1 only):

4. No prior systemic therapy in the locally advanced unresectable/metastaticsetting including chemotherapy, targeted therapy, immunotherapy, orinvestigational agents.

5. Prior PD-1/PD-L1 inhibitor treatment is not permitted in any setting, includingin the neoadjuvant setting.

6. Time between completion of last treatment with curative intent and firstmetastatic recurrence must be ≥ 6 months.

7. Prior systemic therapies (Cohort 2 only):

8. Documentation of PD-L1 positive status

9. Treated with a PD-1/PD-L1 inhibitor for a minimum duration of 4 months in thelocally advanced unresectable/metastatic setting and as the most recenttherapy.

10. Radiation therapy for metastatic disease is permitted. There is no required minimumwashout period for radiation therapy. Patients should be recovered from the effectsof radiation.

11. Archival tumor tissue must be available or a fresh biopsy must be obtained, unlessapproved by the Medical Monitor.

12. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

13. Adequate organ function as demonstrated by normal laboratory values

Exclusion Criteria:

1. Prior treatment with gemcitabine in any setting.

2. Prior treatment with carboplatin in the locally advanced unresectable/metastaticsetting. Prior carboplatin in the (neo)adjuvant/curative setting is permitted as long as itwas completed ≥ 6 months prior to the first metastatic recurrence.

3. Presence of central nervous system (CNS) metastases and/or leptomeningeal diseaserequiring immediate treatment with radiation therapy or steroids.

4. Receipt of any cytotoxic chemotherapy within 14 days prior to the first dose ofstudy drugs.

5. QTcF interval >480 msec at Screening (confirmed in triplicate). For patients withventricular pacemakers, QTcF >500 msec.

6. Known hypersensitivity to carboplatin or other platinum-containing compounds, ormannitol

7. Pregnant or lactating women

8. Prior hematopoietic stem cell or bone marrow transplantation