Normal breast, gross

The normal appearance of female breasts is shown here. The nipple (▼) is surrounded by a darker areola (♦). Some breast tissue extends into the axillary tail of Spence (▪). Breast size is primarily determined by the amount of adipose tissue. There may be some asymmetry in development. Macromastia may occur unilaterally or bilaterally with increased sensitivity to hormonal stimulation, and may be called juvenile hypertrophy when it occurs at the time of puberty. Rarely, a supernumerary breast may produce a subcutaneous mass anywhere from the axilla (∗) to the perineum.

Breast, mammogram

A mammogram uses a low dose of x-rays to visualize the breast parenchyma and shows the pattern of lactiferous sinuses and ducts. In this image is one suspicious density (▼), which could be a carcinoma or just an area of pronounced sclerosis with fibrocystic changes. A mammogram is a useful screening tool to find such lesions and to determine the need for further work-up. A mammogram may detect small lesions not palpable. Women in their 30s begin to have some involution of lobules and adjacent stroma, and the breast tissue becomes more radiolucent from an increased composition of adipose tissue replacing fibrous stroma and lobules.

Normal breast, microscopic

The normal microscopic appearance of female breast tissue is shown, with a larger duct (♦) to the right and lobular units (◀) to the left. A collagenous stroma (▪) extends between the structures. A variable amount of adipose tissue (∗) can be admixed with these elements. During the normal menstrual cycle, after ovulation under the influence of estrogen and increasing progesterone levels, lobular acini increase, epithelial cells become vacuolated, and the interlobular stromal edema increases, leading to increased breast fullness. With menstruation and a decrease in hormone levels, apoptosis of epithelial cells and a reduction in stromal edema occur.

Normal breast, microscopic

The appearance of a normal breast acinus is shown at high magnification. The epithelial cells lining the lumen show apocrine secretion with snouting, or cytoplasmic extrusions (▲), into the lumen. A layer of myoepithelial cells (▼), some of which are slightly vacuolated, is seen just around the outside of the acinus.

Normal breast, microscopic

Immunostaining with antibody to actin shows the red-brown myoepithelial cell layer around the breast acinus. The myoepithelial cells are contractile and very sensitive to oxytocin. After pregnancy and delivery of the infant, suckling by the infant results in release of oxytocin from where it is stored in the posterior pituitary gland. The oxytocin induces myoepithelial cell contraction with expression of milk. Breast secretory activity is driven by prolactin from the anterior pituitary. The initial peripartum secretions low in lipid but high in protein, including maternal immunoglobulins, are known as colostrum .

Normal breast, microscopic

The normal microscopic appearance of female breast tissue is shown here with a terminal duct lobular unit. Note the cluster of lobules lined by epithelial cells that show focal dark brown positivity for estrogen receptor (ER) with immunohistochemistry identifying this steroid hormone receptor in cell nuclei. Normal breast tissue is responsive to estrogen and progesterone. Assessment of estrogen and progesterone receptors is done on tissues removed by biopsy or surgery to evaluate the biologic characteristics of breast carcinomas. Carcinomas that are hormone sensitive may respond to anti-hormonal therapy.

Normal lactating breast, microscopic

The female breast during pregnancy undergoes hyperplasia and hypertrophy so that after birth, lactation can occur. Under the influence of estrogen, terminal ducts and ductal epithelium proliferate, and progesterone promotes development of increased acini in the lobular units. Lobular acini filled with pink-appearing secretions (♦) are seen here. The breast, a modified sweat gland, secretes by budding off of portions of cell cytoplasm (apocrine secretion) to form breast milk with high lipid content. After delivery, estrogen and progesterone levels decrease, increasing the lactogenic effect of prolactin. The acinar epithelial cells become vacuolated with increased secretions.

Acute mastitis, microscopic

While breastfeeding an infant, usually in the first month, the skin of the breast may become irritated, tender, and inflamed. This skin may fissure, predisposing to infection with entry of microorganisms into underlying breast tissue. Acute mastitis typically involves just one breast and is most often caused by bacterial organisms such as Staphylococcus aureus, although streptococci can produce this condition, with neutrophilic infiltrates (▼) seen here microscopically in an acinus. If untreated by antibiotic therapy, spread of infection, abscess formation, and reduction in lactation can occur.

Breast abscess, gross

During lactation, or at other times with dermatologic conditions that allow cracks and fissures to form in the skin of the nipple, or milk stasis occurs with alteration of the microbiome, infectious organisms can invade into breast and result in acute inflammation, and this may progress to breast abscess (♦) formation. The most common organism is S. aureus . Organization with fibrous scar formation around the abscess can form a firm mass that can mimic a carcinoma on physical examination, by mammography, and grossly in the resected tissue specimen.

Fat necrosis, microscopic

The most common etiology of fat necrosis of breast is trauma from external blunt force or from surgical procedures. The resulting lesion can be a localized, firm area with scarring that can mimic a breast carcinoma. Microscopically, fat necrosis consists of irregular steatocytes with loss of their peripheral nuclei, intercellular pink amorphous necrotic material, and inflammatory cells, including macrophages and foreign body giant cells responding to formation of the necrotic debris. In this view of fat necrosis at high magnification, clusters of lipid-laden macrophages (▲) are seen among residual adipocytes (∗).

Breast implant, CT and gross

The chest CT scan in the left panel reveals bilateral silicone breast implants (♦). These implants have induced the formation of a fibrous capsule that has partially calcified (◀). The thin connective tissue capsule (▶) around a silicone breast implant is shown grossly in the right panel . Note the overlying skin and adipose tissue at the upper left, with the chest wall below the implant and to the right. This is a typical capsule that is pliable and nondeforming, without scarring.

Breast implant capsule, microscopic

Microscopic examination of the fibrous capsule from a silicone breast implant often reveals the refractile silicone material (▲) as shown here because this material gradually leaks out from the implant into surrounding connective tissues. This process induces a foreign-body granulomatous response (▼). This is a localized reaction not associated with systemic disease. The fibrosis with scar formation around a breast implant may produce deformity and pain in some women. Rupture of an implant is uncommon.

Fibrocystic changes, gross

A 1.5 cm parenchymal breast cyst (▲) is shown. Its presence led to palpation of an ill-defined, but movable, focal “lump” in the breast to be distinguished from other lesions, including carcinoma. Sometimes, fibrocystic changes, particularly in women of childbearing age, produce a more diffusely lumpy breast with one or more mammographic densities, with or without calcifications. Fine-needle aspiration of fluid from a cyst found in conjunction with fibrocystic changes typically yields benign-appearing cells seen on cytologic preparations, and the cyst may collapse and disappear following aspiration.

Fibrocystic changes, microscopic

The appearances of fibrocystic changes in breast include irregular, cystically dilated ducts (▪) and intervening stromal fibrosis (♦). The cysts are lined by uniform, benign, cuboidal to columnar epithelial cells. This is a “nonproliferative” breast change. Fibrocystic changes account for most breast lumps that are found in women of reproductive years, particularly between the age of 30 and menopause. These changes may produce palpable breast lumps, are often bilateral, but not always symmetric.

Fibrocystic changes, microscopic

Additional breast fibrocystic changes are shown, including the irregular duct and lobule size in the left panel . There is prominent apocrine change with abundant pink-staining cytoplasm (▲) of tall columnar epithelial cells lining the cysts in the right panel . These appearances are benign. Such changes are most common in premenopausal women and may be associated with premenstrual breast tenderness.

Sclerosing adenosis, microscopic

Prominent sclerosing adenosis, one of the proliferative breast diseases and a feature that is often seen in association with fibrocystic changes, is shown by the appearance of a proliferation of small ducts in a fibrous stroma as well as cystically dilated ducts. Microcalcifications (◀) can be present. The number of acini per terminal duct is more than double the number found in normal lobules. This lesion may produce a palpably firm and irregular mass. Although benign, the gross and mammographic appearance may mimic carcinoma, and it can be difficult to distinguish from carcinoma on frozen section of a biopsy specimen.

Intraductal papilloma, microscopic

This small papillary lesion appears within a benign but dilated breast duct, typically in one of the large main lactiferous ducts beneath the areola, where it can be palpated as a lump near the nipple. The epithelial cells show no atypia, and there is a fine pink collagenous stroma (♦) within branching fibrovascular cores of this papilloma. There can be associated proliferative and nonproliferative breast changes. An intraductal papilloma may be associated with a serous or bloody nipple discharge, or it may cause some nipple retraction.