CCL2 and breast cancer: PTEN loss-activated NF-κB signaling and increased expression of the chemokine CCL2 in breast cancer cells (Fig. 1b(l), and the CCL2+ cancer cells recruited macrophages expressing the receptor for CCL2 (CCR2) (Fig. 1b(m)), resulting in the promotion of brain metastasis outgrowth after cancer cell extravasation [41].