Adult mammary stem cells are multipotent cells which are committed to give rise to cells with a specific function. These cells produce a lineage of daughter cells with a unidirectional terminal differentiation process. Mammary gland adult stem cells are slow cycling cells with the ability to respond to environmental cues and propagate additional stem cells or differentiate along a specific cell lineage. Once the stem cell commits to differentiation, it enters a brief period of rapid proliferation. Asymmetrical cell division generates one daughter stem cell and one progenitor cell. This process allows for the maintenance of a stem cell pool for future growth while simultaneously generating a differentiated