CXCR4 and neoplasm: In addition to contributing to tumor-stroma interaction, CXCR4 is also expressed in a key cell type in the tumor microenvironment, cancer stem cells (CSCs), and in particular it has been proposed as a marker for pancreatic CSCs (PaCSCs), along with CD133 and epithelial cell adhesion molecule (EpCAM), among others [17].