Mammary stem cells: the root of breast cancer?

Tissue-specific stem cells play a key role in organ homoeostasis. They are relatively well characterized in systems which undergo constant proliferation and production of differentiated cells, including the haemopoietic system, skin and intestine. However, little is known about the role and regulation of stem cells in the mammary gland. This review briefly summarizes the current understanding of the role of breast-specific stem cells in normal and cancerous tissues, and how this may identify new targets for breast cancer prevention and therapy.