CCL2 recruits inflammatory monocytes to facilitate breast-tumour metastasis

Macrophages are abundant in tumours, where they promote tumorigenesis and metastasis. Jeffrey Pollard and colleagues now identify inflammatory monocytes as a precursor population for the macrophages that promote breast cancer metastasis to the lung or bone. These cells are recruited through the cytokine CCL2 and promote tumour-cell extravasation (by producing the signal protein VEGF) and the seeding of metastases. These findings can explain the poor prognosis for breast cancer patients with elevated expression of CCL2.