Cancer stem cells and EMT in carcinoma

The majority of deaths from carcinoma are caused by secondary growths that result from tumour invasion and metastasis. The importance of epithelial-to-mesenchymal transition (EMT) as a driver of invasion and metastasis is increasingly recognised, and recent evidence has highlighted a link between EMT and the cancer stem cells that initiate and maintain tumours and have also been implicated in invasion and metastasis. Here, we review cancer stem cells and their link with EMT, and explore the importance of this link in metastasis and therapeutic resistance of tumours. We also discuss new evidence from our laboratory demonstrating that cancer stem cells display a remarkable phenotypic plasticity that enables them to switch between an epithelial phenotype that drives tumour growth and an EMT phenotype that drives metastasis. As successful therapies must eradicate cancer stem cells in all their guises, the identification of sub-types of cancer stem cells that display therapeutic resistance and phenotypic plasticity has important implications for the future design of therapeutic strategies. The ability to assay the responses of different cancer stem cell phenotypes in vitro holds promise for the rapid development of a new generation of targeted therapies that fulfil this objective.