CXCR6 and cancer: Increasing evidence has shown that CXCL16/CXCR6 chemokine axis plays multifaceted roles in a variety of cancers, including three major aspects of their activities: (1) CXCL16/CXCR6 functions as a regulator in migration and proliferation of a variety of cancer cells[3, 33-35]; (2) CXCR6 functions as a newly defined biomarker of tissue-specific stem cell [16]; (3) regulating angiogenic processes [15].