Breast stem cells and cancer.

Recent results have increased our understanding of normal stem cells and the signalling pathways which regulate them during the development of the mammary gland. Tumours in many tissues are now thought to develop from dysregulated stem cells and depend on activated stem cell self-renewal pathways such as Notch for their tumourigenic capacity. These cancer stem cells are recognised by specific cell surface proteins that they express and their capacity to grow tumours in vivo or spheres in vitro. We have described human breast DCIS mammospheres grown from cancer stem cells and demonstrated their dependence on the EGF and Notch receptor pathways. Stem cell self-renewal pathways such as these may represent novel therapeutic targets to prevent recurrence of pre-invasive and invasive breast cancer.