Metastasis: New insights into organ-specific extravasation and metastatic niches

The appearance of clinically detectable metastases is the end-point of a complex set of biological processes only few cancer cells are capable to complete. Metastatic colonization comprises the most inefficient metastatic steps as it requires a fine-tuned crosstalk between the disseminated cancer (stem) cells and their host microenvironment. The origin of the cancer cell and its intrinsic properties are factors that together with the organ microenvironment and circulation patterns determine the site of metastatic spread, the dormancy period and the extent of metastasis formation. Recent advances provide novel insights into the molecular components required for organ-specific infiltration, the composition of growth-supportive metastatic niches in different tissues and the cancer cell-niche crosstalk.