This is particularly clear in the stromal compartment, where cancer-derived exosomes can activate fibroblasts through the transfer of molecules, such as transforming growth factor β (TGF-β).16, 17, 18, 19 Fibroblast activation leads to the deposition of extracellular matrix (ECM), tumor fibrosis, and metastasis.20 Here, TGFB1 is linked to cancer.