Second, our data demonstrating the complete inactivity of CXCR4 and CCR7 receptors in non-metastatic cells paints a more complex picture suggesting that inherent differences in breast cancer cells are likely to be important determinants of CXCR4-CCR7 receptor heterodimerisation in the context of tumour progression. This evidence concerns the gene CXCR4 and breast carcinoma.