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). This evidence concerns the gene CXCR4 and cancer.