Metastasis: an early event in cancer progression

Metastasis is the leading cause of death for a majority of cancer patients, and thus the need to understand the biology of metastasis becomes increasingly acute. When metastasis is initiated in tumor progression remains obscure. Better understanding of mechanisms regulating acquisition of metastatic ability in tumor cells will provide novel therapeutic targets and prevention of metastasis in clinics accompanied with the treatment of the primary tumor might be helpful in reducing metastasis-related mortality. A literature search was performed in multiple electronic databases. Research papers from clinical reports to experimental studies on metastasis were analyzed. The article discusses tumor heterogeneity and genomic instability in the context of metastasis and tumor cell dissemination. And then we review biological mechanism of metastasis at an early stage in both intracellular (CSCs and CTCs) and extracellular (microenvironment) context. Finally, current development of anti-metastatic therapies is summarized. Metastasis could be initiated at an early point of tumor progression. Therefore, early intervention on metastasis should be applied among cancer patients in clinical settings.