Our present and previous findings5, 6, 7 indicate that pleural tumour-originated CCL2 mobilizes two distinct cell populations from the bone marrow: mast cells and CD11b+Gr1+ cells41, 42, both known to respond to CCL2 (refs 7, 25), to facilitate breast cancer metastasis to the lungs34, and to sustain tumour growth by promoting angiogenesis28. Here, CCL2 is linked to neoplasm.