Tavo and Pembrolizumab With or Without Chemotherapy in Patients With Inoperable Locally Advanced or Metastatic TNBC

The study will include a screening period, treatment period (up to 2 years), a long-term follow-up period, and a survival follow-up period. Participants will be followed for disease status and survival for up to a total duration of 5 years from the time of first dose of study treatment. Eligible subjects with accessible lesions will be treated with TAVO-EP on Days 1, 5 and 8 every 6 weeks for up to 18 weeks. Pembrolizumab IV will be administered at a dose of 200 mg on Day 1 every 3-weeks for up to 35 cycles (Q3W) or 400 mg on Day 1 every 6 weeks for up to 18 cycles (Q6W). Eligible subjects will be enrolled in one of the following cohorts. * Cohort 1 is a single-arm study of intratumoral TAVO-EP and pembrolizumab (Q3W) in participants with TNBC and at least 1 line of prior systemic therapy in the advanced or metastatic setting. * Cohort 2 is a single-arm study of intratumoral TAVO-EP and pembrolizumab along with treatment with an approved chemotherapy per standard of care (either nab-paclitaxel (Abraxane®)or gemcitabine (Gemzar®) plus carboplatin (Paraplatin®)) in participants with TNBC and no prior systemic therapy in the advanced or metastatic setting. Participants enrolled on or after Protocol Version 7 will have baseline disease PD-L1 negative status defined as Dako 22C3 assay CPS \<10. For participants in Cohort 2 receiving nab-paclitaxel, the schedule for nab-paclitaxel is a separate 28-day cycle. The dosing regimen of nab-paclitaxel is 100 mg/m2 IV over 30 minutes on Days 1, 8, and 15 of each 28-day cycle. For participants in Cohort 2 receiving gemcitabine plus carboplatin, the dosing regimen is gemcitabine 1000 mg/m² plus carboplatin area under the curve (AUC) 2 IV on Days 1 and 8 every 21 days.