REVIEW Anatomy of the Human Mammary Gland: Current Status of Knowledge FOTEINI HASSIOTOU 1,2 AND DONNA GEDDES 1 * 1 Hartmann Human Lactation Research Group, School of Chemistry and Biochemistry, Faculty of Science, The University of Western Australia, Crawley, Western Australia, Australia 2 School of Anatomy, Physiology and Human Biology, Faculty of Science, The University of Western Australia, Crawley, Western Australia, Australia Mammary glands are unique to mammals, with the specific function of synthe- sizing, secreting, and delivering milk to the newborn. Given this function, it is only during a pregnancy/lactation cycle that the gland reaches a mature devel- opmental state via hormonal influences at the cellular level that effect drastic modifications in the micro- and macro-anatomy of the gland, resulting in remodeling of the gland into a milk-secretory organ. Pubertal and post-puber- tal development of the breast in females aids in preparing it to assume a func- tional state during pregnancy and lactation. Remarkably, this organ has the capacity to regress to a resting state upon cessation of lactation, and then undergo the same cycle of expansion and regression again in subsequent pregnancies during reproductive life. This plasticity suggests tight hormonal regulation, which is paramount for the normal function of the gland. This review presents the current status of knowledge of the normal macro- and micro-anatomy of the human mammary gland and the distinct changes it undergoes during the key developmental stages that characterize it, from em- bryonic life through to post-menopausal age. In addition, it discusses recent advances in our understanding of the normal function of the breast during lac- tation, with special reference to breastmilk, its composition, and how it can be utilized as a tool to advance knowledge on normal and aberrant breast devel- opment and function. Finally, anatomical and molecular traits associated with aberrant expansion of the breast are discussed to set the basis for future com- parisons that may illuminate the origin of breast cancer. Clin. Anat. 26:29–48, 2013. V V C 2012 Wiley Periodicals, Inc. Key words: breast; mammary gland; anatomy; histology; stem cells; lactocytes; lactation; breast cancer INTRODUCTION The mammary gland is an organ unique to the class Mammalia, with the specific function to synthe- size, secrete, and deliver milk to the newborn upon demand for its optimal nourishment, protection, and development (Medina, 1996). Milks from differ- ent mammalian species vary in composition and are uniquely appropriate for the species for which the milk was synthesized. In humans, the life cycle of the female mammary gland is epitomized by drastic *Correspondence to: Donna Geddes, Hartmann Human Lactation Research Group, School of Chemistry and Biochemistry, Faculty of Life and Physical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia. E-mail: donna.geddes@uwa.edu.au Grant sponsors: Medela AG, Women and Infants Research Foundation. Received 2 July 2012; Accepted 16 August 2012 Published online 19 September 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ca.22165 V V C 2012 Wiley Periodicals, Inc. Clinical Anatomy 26:29–48 (2013)