Both cohorts will receive the identical doses and treatment schedules of decitabine and pembrolizumab followed by a standard neoadjuvant chemotherapy regimen. Both cohorts will receive 4 cycles of dose-dense AC followed by 12 doses of weekly paclitaxel. Paclitaxel will be combined with carboplatin for Cohort A (TNBC). The primary safety objective will be to evaluate the safety and toxicity of sequential decitabine plus pembrolizumab followed by dose-dense AC, weekly paclitaxel (or paclitaxel plus carboplatin) administered as neoadjuvant therapy. If the breast tumor is resectable following completion of all protocol therapy, breast-conserving surgery or mastectomy and axillary surgical staging (either sentinel node biopsy and/or axillary dissection) will be performed.