[NORMAL BREAST HISTOLOGY]. Breast can be considered a modified skin appendage in Mammalians producing milk for the nourishment of the newborn. The milk is discharged from a collection of 10-20 large ducts opening through pores in the nipple during lactation. Each large duct, also called lactiferous duct, branches out deep into the breast tissue forming what is called a breast lobe. Thus, a breast consists of about 10-20 inter-anastomosing lobes separated from each other by varying amounts of fibro-adipose tissue. This photomicrograph shows six (6) lactiferous ducts (arrows) that run from the nipple to branch down into successive smaller ducts until the formation of “terminal duct lobular unit (TDLU).”
.jpeg?Width=600&Height=450&Format=4 "Normal breast")
[NORMAL BREAST HISTOLOGY]. Cross section at the level of nipple shows lactiferous ducts with a scalloped appearance, possibly related to the origin of segmental branches. The duct system resembles any other dichotomously branching system of glands where a single large duct successively branches down to its most terminal level. The lactiferous duct gives rise to segmental ducts, which in turn gives rise to sub-segmental branches and so on until a terminal duct lobular unit is formed. The large lactiferous duct is the site for solitary papilloma and duct ectasia with nipple discharge.
[NORMAL BREAST HISTOLOGY]. The lactiferous duct is enlarged and dilated near the base of the nipple to what is called a lactiferous sinus (arrow). This sinus functions to hold milk and discharges it upon contraction by the surrounding smooth muscles. The sinus continues with ampullae near the nipple surface.
[NORMAL BREAST HISTOLOGY]. The nipple and subareolar region contains abundant bundles of smooth muscle fibers (arrow) enmeshed in dense collagenous stroma. The contraction of these muscle fibers is responsible for nipple erection and milk discharge.
Image name – Normal-breast-histology-(4-BT04H -2)
[NORMAL BREAST HISTOLOGY]. As the lactiferous duct runs deeper into the breast tissue it branches out into segmental branches which are smaller but still lined by two layers (arrow): the luminal epithelial layer of cuboidal to columnar cells and an outer myoepithelial contractile layer.
[NORMAL BREAST HISTOLOGY]. Higher magnification of the lactiferous-segmental duct shows an inner luminal epithelial layer of cuboidal to columnar cells (arrowhead) and an outer myoepithelial contractile layer (arrow).
[NORMAL BREAST HISTOLOGY]. This photomicrograph depicts a sub-segmental duct (arrow) giving rise to multiple “Terminal duct lobular units (arrowheads)” embedded in dense stroma. The TDLU are terminal units of the duct system.
[NORMAL BREAST HISTOLOGY]. This photomicrograph depicts another view (cross section) of a sub-segmental duct (arrow) giving rise to multiple “Terminal duct lobular units (arrowheads)” embedded in dense stroma.
[NORMAL BREAST HISTOLOGY]. This photomicrograph shows a “Terminal duct lobular unit” which is a structural and functional unit of the breast. In essence, one terminal duct (arrow) of the breast duct system gives rise to a collection of smaller ductules (arrowhead) called a “Lobule” which ‘produces’ milk to be discharged through the duct system. Most cancers are thought to arise from cells of these TDLUs.
[NORMAL BREAST HISTOLOGY]. A lobule of a TDLU is shown (arrowhead) without an obvious terminal duct entering/leaving this unit. Note that a TDLU is surrounded by a dense collagenous stroma (arrow) but the stroma inside the lobule is not as dense as outside. A breast is usually made up of about 10-20 lobes and each lobe in turn can contain up to several thousand lobules. Each lobule can contain 20-200 smaller ductules/acini. The number of breast lobes, lobules in each lobe, and ductules/acini in each lobule vary greatly.
.jpeg?Width=600&Height=450&Format=4 "Normal breast")
[NORMAL BREAST HISTOLOGY]. A lobule contains 20-200 smaller ductules/acini which are formed by successive branching of the terminal duct. An intralobular ductule is shown to giving rise to five terminal ductules/acini at this plane of section (arrows). The terminology “acinus” for theses blindly-ended branches may be used when they form dilated gland-like structures. For terminal structures that do NOT form dilated ends may be best referred to as terminal ductules. Note the loose myxomatous intralobular stroma which contains fibroblasts, small lymphocytes, and plasma cells (big yellow arrow).
.jpeg?Width=600&Height=450&Format=4 "Normal breast")
[NORMAL BREAST HISTOLOGY]. This photomicrograph shows three acini with lumens (long arrow). Each acinus is lined by two layers: an outer complete layer of myoepithelial cells with clear cytoplasm (arrowheads) and an inner layer of cuboidal to columnar epithelial cells (curved arrow). Note that each acinus is enveloped in a basement membrane and the surrounding stroma contains fibroblasts, lymphocytes, and plasma cells.
[NORMAL BREAST HISTOLOGY]. This immunohistochemical stain for S-100 protein shows a complete outer layer of myoepithelial cells (arrowhead) but the inner cuboidal to columnar epithelial cells are not reactive for this antigen.
NORMAL BREAST HISTOLOGY]. This immunohistochemical stain for mammaglobin protein shows no staining in the outer layer of myoepithelial cells (arrowhead) but the inner cuboidal to columnar epithelial cells are strongly positive for this antigen.
NORMAL BREAST HISTOLOGY]. This immunohistochemical stain for estrogen receptor protein shows no staining in the outer layer of myoepithelial cells (arrowhead) but the inner cuboidal to columnar epithelial cells are strongly positive for this antigen.
NORMAL BREAST HISTOLOGY]. This immunohistochemical stain for progesterone receptor protein shows no staining in the outer layer of myoepithelial cells (arrowhead) but the inner cuboidal to columnar epithelial cells are strongly positive for this antigen.