IL6 and cancer: A more complex regulatory loop between cancer and immune cells has been described in in vitro co-culture model of colorectal cancer: the secretion of IL-6 from immune cells promotes invasiveness of cancer cells, which in turn induces immune-related IL-6 production and miR-21 release through the tumor-derived secretion of miR-21 and miR-29b in the tumor microenvironment [164].