Purpose: Tumours are composed of a heterogeneous cell population. Cancer stem cells, which make up a minor fraction of a tumour, may be the cells that initiate and sustain tumour growth. Cancer stem cells are believed to share many properties with normal stem cells that render them relatively insensitive to classical radio- and chemotherapy.
Conclusions: We discuss what those (cancer) stem cell properties are and how the interactions with the microenvironment--'the niche'--control those aspects of (cancer) stem cell biology. We also describe possible strategies to target cancer stem cells in order to prevent cancers from escaping therapy.