Chemokine (C–C motif) ligand 3 (CCL3) (also known as macrophage inflammatory protein 1 α (MIP‐1α)), is associated with metastasis of various tumor types such as renal cell and colorectal cancer,[31, 32, 33] and was shown to mediate macrophage retention in the metastatic sites of breast cancer.[35] Since the cytokine array analysis revealed a specific increase of CCL3 in the HM‐macrophage coculture, we next investigated the role of CCL3 in the crosstalk. The gene discussed is CCL3; the disease is breast cancer.