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

This study will have two separate cohorts (Cohort 1 and Cohort 2). Both cohorts will follow the same general study conduct/design with similar primary and key secondary endpoints and identical treatment arms. * Cohort 1 will evaluate patients receiving first-line therapy, regardless of programmed death-ligand 1 (PD-L1) status, who are programmed cell death protein 1 (PD-1)/PD-L1 inhibitor therapy naïve. * Cohort 2 will evaluate PD-L1 positive patients receiving second-line therapy following prior PD-1/PD-L1 inhibitor therapy in the locally advanced unresectable/metastatic setting.