Systemic hormones are key regulators of postnatal mammary gland development and play an important role in the etiology and treatment of breast cancer. Mammary ductal morphogenesis is controlled by circulating hormones, and these same hormones are also critical mediators of mammary stem cell fate decisions. Recent studies have helped further our understanding of the origin, specification, and fate of mammary stem cells during postnatal development. Here we review recent studies on the involvement of hormone receptors and several transcription factors in mammary stem/progenitor cell differentiation and lineage commitment.
