The Role of Cancer Stem Cells in Tumour Radioresponse

In order to achieve complete tumour cure after radiotherapy, it is mandatory that all cancer stem cells (CSCs) are being killed. Therefore, new anti-cancer treatments should not only be directed against the bulk of the tumour but also have to target those tumour cells, which are expressing putative CSC markers since they highly determine tumour radioresistance as discussed in this chapter. This is further being influenced by other factors such as the tumour microenvironment, epithelial-mesenchymal transition as well as changes during the course of radio(chemo)therapy. Together with established parameters such as the tumour volume for primary radio(chemo)therapy or the human papilloma virus infection status for head and neck squamous cell carcinoma, the utilization of putative CSC markers may help to predict radiotherapy outcome and allow for patient stratification for individualized treatment strategies.