The Emerging Picture of Human Breast Cancer as a Stem Cell-based Disease

There are increasing data supporting the existence of a cell hierarchy within the mammary gland. At the top or this hierarchy a small population of cells with self-renewal properties maintains the tissue architecture and remodeling, and they are known as stem cells. Also, recent evidences indicate that breast cancer is originated and maintained by its own cancer stem cells reminding the normal mammary gland. The existence of this small population of cells with self-renewal capability has important biological and clinical significances. So, the interpretation of tumors as hierarchical cellular structures has changed our vision of the breast cancer scenario. Here, we review the current knowledge about normal and breast cancer stem cells, and their implications in cancer development, together with their consequences in breast cancer susceptibility, dissemination and treatment response.