CXCR6 and cancer: The decreasing order of expression levels was as follows: CXCR4, CXCR7, CXCR2, CXCR6, CXCR5, CXCR3, and CXCR1. Although, CXCR2 expression is down-regulated in samples from most types of cancers compared to samples from normal subjects, it was found to be upregulated in AML (Figure 1B).