Development of the human breast

Abstract

Mammalia are so named based on the presence of the mammary gland in the breast. The mammary gland is an epidermal appendage, derived from the apocrine glands. The human breast consists of the parenchyma and stroma, originating from ectodermal and mesodermal elements, respectively. Development of the human breast is distinctive for several reasons. The human breast houses the mammary gland that produces and delivers milk through development of an extensive tree-like network of branched ducts. It is also characterized by cellular plasticity, with extensive remodeling in adulthood, a factor that increases its susceptibility to carcinogenesis. Also, breast development occurs in distinct stages via complex epithelial-mesenchymal interactions, orchestrated by signaling pathways under the regulation of systemic hormones. Congenital and acquired disorders of the breast often have a basis in development, making its study essential to understanding breast pathology.

Keywords: Tanner staging; breast embryology; mammary gland development.

Fig. 1

Development of the mammary gland. (A) Ventral view of an embryo at 28-days gestation showing mammary crests. (B) Similar view at 6-week gestation showing the remains of the mammary crests. (C) Transverse section of a mammary crest at the site of the developing mammary gland. (D–F) Similar sections showing successive stages of breast development between the 12^th week of gestation and birth. (Reprinted with permission from Moore KL, Persaud TVN, Torchia MG, The Developing Human: Clinically Oriented Embryology. 9^th ed. 2013 Copyright Elsevier).

Fig. 2

Tanner stages of breast development. (Reprinted with permission from Marshall WA, Tanner JM. Variations in pattern of pubertal changes in girls. Arch Dis Child 1969;44:291–303. Copyright BMJ Publishing).

Fig. 3

Pubertal breast development. (A) Carmine-stained whole-mount preparation of the advancing edge (arrow) of the parenchyma from a 13-year-old girl. (B) Hematoxylin- and eosin-stained developing breast of 13-year-old girl showing solid end bud-like structures (denoted teb) and lateral buds (arrows). (C) Coronal section of breast of 15-year-old girl. (D) Higher power view of panel C, arrows indicate ducts and unfilled arrowheads indicate duct termini. (E) Histology section of the peripheral region of parenchyma seen in (C). teb denotes terminal end bud. (F) Carmine-stained whole mount preparation of breast from 18-year-old nulliparous woman. A segmental duct divides into two subsegmental ducts (ss), which then lead to the terminal duct lobular units (tdlu). (G) Electron micrograph of a normal adult subsegmental duct. The bilayered histology with paler luminal cells (l), darker basal (myoepithelial) cells (m) is evident. An intraepithelial lymphocyte (arrow) is also seen. (H) Electron micrograph of a terminal duct lobular unit showing two basal clear cells. These have microfilaments in the basal part of the cell (large arrows) and desmosome attachments with the luminal cells (small arrows). (Reprinted with permission from Howard BA, Gusterson BA. Human breast development. J Mammary Gland Biol Neoplasia 2000;5(2):119–137. 2000 Copyright Springer).