(Pre-)clinical research has revealed that gut bacteria influence cancer onset, progression and therapy response, although precise mechanisms remain unknown. Gut bacteria release bacterial extracellular vesicles (BEV), membrane-enclosed particles containing a variety of biomolecules that can be recognized by pattern recognition receptors on host cells. Recently, my host lab discovered that BEV are systemically present in cancer patients with impaired intestinal barrier integrity. This discovery prompts the novel concept of exploring BEV uptake and function in the tumor microenvironment (TME). I aim to explore BEV uptake and function by combining cutting-edge technologies and models that mimic with increasing complexity the TME as found in cancer patients. For this purpose, I will focus on models of triple-negative breast cancer (TNBC) since my preliminary data show that systemic BEV accumulate in TNBC patients during neo-adjuvant chemotherapy. I will implement state-of-the-art super-resolution microscopy for in vitro and ex vivo evaluation of BEV uptake mechanisms. Furthermore, I will scrutinize BEV function ex vivo and in vivo, using complementary single-cell technologies. I am confident that this biological and technological driven approach will steer our understanding of BEV in cancer progression with the potential to ultimately unlock novel clinical applications.