CCL21 and breast cancer: Because the interaction of CCL21 with its receptor CCR7 has been linked to lymph node metastasis of breast cancer and other tumor types (for review see: [34]), we first investigated whether hybrid cell lines respond to CCL21 with an activation of CCR7 specific signal transduction cascades including PI3K/AKT, MAPKp42/44 and PLC-β/γ signaling [27].