To investigate whether cells present in the tumor microenvironment can influence metastatic TNBC cell behavior and expression of CYP2C19, FABP4, and FABP5, we used an in vitro co-culture model, selecting some of the representative tumor stromal cells, namely fibroblasts, adipocytes, and cells of monocytic lineage known to influence lipid homeostasis in breast cancer cells [8,43,44,45,46]. This evidence concerns the gene CYP2C19 and breast cancer.