CXCR4 and breast cancer: To address how biochemical inputs regulate the behavior of tumor cells, we recently reported how conditioning cells with chemotherapeutics and/or cytokines potentiates signaling from CXCL12-CXCR4 and EGF-EGFR through PI3K/Akt/mTOR and Ras/Raf/MEK/ERK9,10 two pathways central for breast cancer progression and metastasis.