For example, colorectal CSCs with a marked potential to form distant metastasis are identified by CD26 and CD44v6 surface expression [99, 116] Further evidence for the unique role of CSCs in the metastatic process comes from the finding that cells expressing these markers (CD26 and CD44v6) can be isolated from the blood of CRC patients as circulating tumor cells (CTCs), and these cells display the ability to form cancers [117]. This evidence concerns the gene DPP4 and cancer.