However, CXCR7 and CXCR4 appear to be co-expressed in some cancers (i.e breast cancer lines like MDA-MB-231 and MCF-7 129), but not in others (recurrent glioblastoma 124), suggesting that only MICs from select types of cancer utilize CXCR7 functions. This evidence concerns the gene ACKR3 and breast carcinoma.