A Study of Sacituzumab With Chemoimmunotherapy to Treat Advanced Triple-Negative Breast Cancer After Prior Therapies

In part 1 of phase 1b, 3 to 6 subjects will be sequentially enrolled starting at dose level 1 and will be assessed for dose limiting toxicities (DLTs). Dose level cohorts for sacituzumab govitecan-hziy are as follows: * Dose level 1: Sacituzumab govitecan-hziy (7.5 mg/kg IV) * Dose level 2: Sacituzumab govitecan-hziy (10 mg/kg IV) * Dose level 1 (if needed): Sacituzumab govitecan-hziy (5.0 mg/kg IV) In part 2 of phase 1b, dose expansion will occur when the RP2D has been determined. An additional 4 subjects may be enrolled, for a total of up to 10 subjects at the RP2D. Following part 2 of the phase 1b portion of the study, the Safety Review Committee (SRC) will meet to determine if enrollment into phase 2 should proceed. In the phase 2 portion of the study, 22 subjects will be enrolled at the RP2D in the first stage of Simon's two stage optimal design. If ≥ 9 of 22 subjects exhibit a confirmed response, the study will proceed to the second stage. If the study proceeds to the second stage, an additional 41 subjects will be enrolled for a total of 63 subjects in the phase 2. If ≥ 27 of the 63 subjects exhibit a confirmed response, the combination therapy will be considered for further development. All subjects may receive up to 17 cycles (ie, 51 weeks) of treatment administered in 3-week cycles.