DPP4 and cancer: Our previous work demonstrated a subpopulation of CD26(+) cancer stem cells (CSCs) uniformly present in both the primary and metastatic tumors in CRC patients with liver metastasis and revealed that the presence of CD26(+) CSCs in primary tumors predicted distant metastasis, which led to the development of distant metastasis in a mouse model and was associated with invasiveness and chemoresistance [12].