Most importantly, the levels of this heterodimeric chemokine receptor, as opposed to that of its constituent protomers, is most likely responsible for the augmented CXCR4 and CCR7 functional activity in metastatic breast tumour cells, since both the CXCR4 and CCR7 individual protein expression levels were comparable between the normal and breast cancer tissues relative to the area of the mammary epithelial compartment (Supplementary Figure S3B). The gene discussed is CXCR4; the disease is breast cancer.