Research has been increasing in recent years into the application of stem cell biology to clinical medicine, particularly its role in the evolution and metastasis of tumours. Stem cells may be the target cell for malignant transformation, and tumour formation could be considered a disorder of stem cell self-renewal pathways. Cancer stem cells have been identified in acute myeloid leukaemia and in breast and central nervous system tumours. Cancer stem cells may have a specific role in tumour metastasis, and their understanding may provide insights into the development of predictive and prognostic markers and specific therapeutic interventions.