Molecular insights into tumour metastasis: tracing the dominant events.

Metastasis of malignant cells to vital organs remains the major cause of mortality in many types of cancers. The tumour invasion-metastasis cascade is a stepwise and multistage process whereby tumour cells disseminate from primary sites and spread to colonize distant sites through the systemic haematogenous or lymphatic circulations. The general steps of metastasis may be similar in almost all tumour types, but metastasis to different tissues seems to require distinct sets of regulators and/or an 'educated' microenvironment which may facilitate the infiltration and colonization of tumour cells to specific tissues. Moreover, interactions of tumour cells with stromal cells, endothelial cells, and immune cells that they encounter will also aid them to gain survival advantages, evade immune surveillance, and adapt to the new host microenvironment. Due to the high correlation between tumour metastasis and survival rate of patients, a deeper understanding of the molecular participants and processes involved in metastasis could pave the way towards novel, more effective and targeted approaches to prevent and treat tumour metastasis. In this review, we provide an update on the regulation networks orchestrated by the dominant regulators of different stages throughout the metastatic process including, but not limited to, epithelial-mesenchymal transition in local invasion, resistance to anoikis during migration, and colonization of different distant sites. We also put forward some suggestions and problems concerning the treatment of tumour metastasis that should be solved and/or improved for better therapies in the near future.