ACKR3 and cancer: The chemokine CXCL12 and two of its receptors, CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3), together play critical roles in central nervous system, cardiac, and vascular development, as well as in cancers where they contribute to angiogenesis, tumor growth, invasion, and metastasis (1, 2).