The tumor microenvironment of colorectal cancer liver metastases: Molecular mediators and future therapeutic targets

The liver has evolved to maintain tissue homeostasis and a state of immune-unresponsiveness in the face of constant exposure to food-derived and commensal microbial products entering through the portal circulation. This is achieved by the unique properties of cells residing in the liver that function to dampen adaptive immune responses. Here we will survey the unique features of the liver microenvironment that contribute to this general state of immune-tolerance and render the liver particularly “hospitable” to incoming metastatic cancer cells. The diverse cell types and unique liver ECM, which collectively control the progression of metastasis and can act to curtail or promote the process, will be described and recent insight into their respective roles highlighted.