CXCR6 and prostate cancer: Activation of CXCR6 by CXCL16 leads to increased expression and secretion of matrix metalloproteinases (MMP) in many types of cancer cells, such as breast cancer cells [110], gastric cancer cells [118], hepatocellular carcinoma cells [120], non-small cell lung cancer cells [77], in highly invasive ovarian cancer cells (not in less invasive cells) [113], papillary thyroid cancer cells [90], and prostate cancer cells [29,115,117].