How and when do tumor cells metastasize

摘要: Tumor cells metastasize when they have successfully passed a number of invasion steps. We hypothesize that each step is microecosystem, the basic elements which are neoplastic cells, host and extracellular matrix (ECM). review here molecular pathways with regulatory function in these microecosystems: homotypic cell-cell adhesion molecules counteracting invasion; complexes lytic (pro-)enzymes, their receptors inhibitors regulating focalized breakdown ECM; components, cellular motility factors governing cell migration; heterotypic initiating extravasation, encompassing vasculature sequence: arrest, ECM lysis, allowing survival growth at ectopic sites. conclude delicate balances within microecosystems responsible for temporary repeated events leading to metastasis.