Cancer stem cells and radiotherapy

In clinic, tumor recurrence and metastasis are the major barriers to further improve the overall cancer patients’ survival. The theory of tumor repopulation due to radiation described decades ago is being supported by new experimental data. The heterogeneity of cancer cell populations in a given tumor is recently evidenced by the present of cancer stem cells (CSCs) that are different from other non-CSC tumor cells and maintain unique self-renewal and tumor-initiating phenotypes. The CSCs isolated from many human tumors including the breast cancer stem cells (BCSCs) are demonstrated to hold specific characteristics and are demonstrated to be resistant to an array of anti-cancer agents and radiation therapy. In this chapter, a number of prosurvival pathways and biomarkers found in BCSCs will be discussed. Several prosurvival features including CSCs repopulation, DNA repair ability, as well as the HER2- NFjB-HER2 signaling loop in the radioresistant BCSCs will be illustrated. Further clarification of the specific networks associated with the radioresistant phenotype of BCSCs will shed new light on the molecular mechanism of tumor radioresistance, and will help to generate targets to detect and treat therapy-resistant tumor cells.