Cancer stem cell definitions and terminology: the devil is in the details

This article outlines some of the issues surrounding the terminology used for cancer stem cells (CSCs) and how CSCs are defined, with an aim to develop a consensus. More precise reporting of parameters used to identify CSCs is also recommended to enhance our understanding of CSC biology and to ultimately eradicate these cells in patients. The cancer stem cell (CSC) concept has important therapeutic implications, but its investigation has been hampered both by a lack of consistency in the terms used for these cells and by how they are defined. Evidence of their heterogeneous origins, frequencies and their genomic, as well as their phenotypic and functional, properties has added to the confusion and has fuelled new ideas and controversies. Participants in The Year 2011 Working Conference on CSCs met to review these issues and to propose a conceptual and practical framework for CSC terminology. More precise reporting of the parameters that are used to identify CSCs and to attribute responses to them is also recommended as key to accelerating an understanding of their biology and developing more effective methods for their eradication in patients.