Cancer metastasis: a short account

Tissue-specific cancer stem cells comprise a very small proportion of the cell population of a cancerous tumour. These cells have an undifferentiated phenotype, a relatively unlimited capacity for self renewal, and they divide slowly. Primary tumour cells with a stem cell phenotype are the driving force behind the uncontrolled proliferation of the cancerous tissue, and if they spread to distant sites, they can establish metastases. Cancer metastasis is a multistep process. The orderly sequence of events of the metastatic process comprises invasion of the surrounding normal stroma by cancer cells carrying a cancer stem cell phenotype, invasion of blood or lymphatic vessels, survival in the circulation during transport to a distant site, and establishment of micrometastases with subsequent metastatic growth. Microenvironment-specific chemokines secreted by cells at the candidate tissue site for metastasis attract type-specific tumour cells that express corresponding chemokine receptors. This is the critical mechanism determining the destination of metastatic cells. The subsequent paracrine interactions between the metastatic cells and their new microenvironment are essential for establishment of a metastatic cancer.