CXCR4 and breast cancer: We used the FRET fluorophore pair of Phycoerythrin (PE) as a donor and Allophycocyanin (APC) as an acceptor, which were directly conjugated to anti-CXCR4 and anti-CCR7 monoclonal antibodies respectively, or APC-conjugated IgG as a control, to assess a potential native complex formation between these two receptors in our panel of breast cancer cells.