Stem cells and breast cancer: A field in transit

Evidence that supports the existence of a tumour stem cell for breast cancer has given fresh impetus to the search for an adult mammary epithelial stem cell in the normal breast. Such a cell might be responsible for routine tissue renewal and the massive expansion in epithelial tissue that the breast undergoes during pregnancy, and might be the cell of origin of most, if not all, breast tumours. So, what evidence is there that an adult mammary epithelial stem cell exists, what is its possible identity and what opportunities might the identification of such a cell present for the development of novel therapeutic and prophylactic strategies for treating breast cancer