CXCR4 and cancer: Although the first known activity of CXCR4 was the regulation of HIV- infection and cancer metastasis (Bleul et al., 1997; Helbig et al., 2003; Doi et al., 2018; Shanmugam et al., 2018; Bianchi and Mezzapelle, 2020), CXCR4 is also an abundantly expressed chemokine receptor throughout embryogenesis (Yusuf et al., 2005; Yusuf et al., 2006).