Finally, conditioning of WT mice with CCL2-conjugated exosomes, followed by injection of syngeneic cancer cells, led to a significant (p < 0.05) increase in lung metastasis formation compared to non-conjugated exosomes, while no impact on BC metastasis was noticed in the lungs of CCR2−/− mice (Fig. 5j and k). This evidence concerns the gene CCR2 and breast cancer.