A Cancer Vaccine (STEMVAC) in Combination With Chemotherapy for the Treatment of PD-L1 Negative Metastatic Triple-Negative Breast Cancer

OUTLINE: Patients receive systemic standard of care chemotherapy as determined by their attending medical oncologist. Patients receive 3 priming doses of STEMVAC with sargramostim intradermally (ID) every 21-28 days (7-13 days after each chemotherapy administration or during the off week of weekly chemotherapy), 2 booster STEMVAC/sargramostim doses at 4 and 7 months after 3rd priming dose, and then every 6 months in the absence of disease progression or unacceptable toxicity. Patients also undergo image-guided biopsy, for research purposes, on study, as well as computed tomography (CT) or positron emission tomography (PET) scans and blood sample collection throughout the study. In addition, patients may also undergo image-guided biopsy, for research purposes, during screening. After completion of study treatment, patients are followed up at 21 or 28 days and then every 6 months for 3 years.