The mammary stem cell conundrum: is it unipotent or multipotent?

Exploring the normal biology and regulation of stem cells has the promise to yield insights into the etiological roots and survival of breast cancer cells. Many studies have supported the existence of a multipotent mammary stem cell that regenerates all aspects of glandular development. However, Van Keymeulen and colleagues (2011) illustrated the presence of lineage-restricted unipotent stem cells that self-renew and collaborate in postnatal mammary development, whereas multipotent stem cells were found only during embryonic mammogenesis. This prompts a re-evaluation of currently accepted mammary stem cell dynamics and conceivably its impact on the evolution of different breast cancer subtypes.