Each duct and/or "acinus" is lined by two epithelial cell layers, an inner cuboidal layer, and an outer often less visible myoepithelial layer.

In this low power view, one can see a distorted lobule surrounded by fibrous tissue. The ducts in the center are severely compressed and squeezed into flat shapes that, to the unwary, resemble infiltrating carcinoma. Nearer the periphery the ducts "open up" and have a more normal appearance. Key features that distinguish it from carcinoma are the fact that it is a process that affects single lobules and that it selectively distorts the central part of the lobule.

Epitheliosis is characterized by proliferation of benign epithelial cells filling ducts, a process which tends to be multicentric.

Benign cysts filled by serous fluid often have this blue color when viewed from the outside.

The breast has about 6 to 10 lactiferous duct systems coming from the nipple.on the outside and the epithelium is keratinizing squamous but on the inside it is double layered space cuboidal. There is even a keratin plug covering the duct opening on the outside. The lactiferous duct is wide and to become lactiferous sinus under the nipple. On the inside, a terminal duct terminates as acini. One collecting duct and its terminal ductules.per lobule. Luminal cells of the terminal duct produce milk but those lining the large ducts do not. These secretary units can be seen in agreement during the first few cycles on oral contraceptive (progesterone?) There is also another layer of cells (myoepithelial) that lives on the basement membrane and help eject milk.Breast stroma is mostly fibrous connective tissue and adipose. There are a lymphocytes in the stroma around lobules.Before puberty there are few lobules. After puberty there are more lobules and interlobular stroma. After ovulation during each cycle there is a rise in number of acini, vacuolization, intralobular stroma edema due to rise in progesterone and estrogen. This explains premenstrual sense of fullness. During pregnancy there are more lobules and less stroma but milk production is inhibited by high progesterone. Pregnancy causes permanent increase in size and number of lobules.Milk contains IgA, immune cells, cytokines, and lysozyme.Elderly people have less lobules and just have talked almost like the male breast. Some lobules remain. Radiolucent adipose tissue is seen.

In some women the ducts extend into subcutaneous tissue so it is hard to remove entire breast with a mastectomy. Therefore this procedure does not completely eliminate risk of breast cancer. Most breast disease is seen in the upper outer quadrant of the breast which is the most massive anyway.

Most breast symptoms or lesions are due to benign processes. Common symptoms are pain, palpable mass, nipple discharge. Pain is most common. Diffuse cyclical is normal (hormones) while non-cyclical focal pain may be due to cysts, injury, infections but more often no cause. Palpable mass there is are greater than 2 cm found mostly premenopausal becoming less frequent with age. Rate of malignancy however increases with age. Palpable masses include invasive carcinomas, fibroadenomas, and cysts. Nipple discharge is worrisome when spontaneous and unilateral. Milky discharge from high prolactin (pituitary adenoma), hypothyroid, anovulation, oral contraceptives. Bloody/serous discharge is mostly benign. Bloody discharge and pregnancy from rapid formation of new lobules. More malignancy rib age. Causes of discharge: Large.duct papilloma, cysts, carcinoma.

Mammography improved with age (more fatty tissue, more malignancy). Start screening at age 40 but younger women need screening if family history of breast cancer. Mammography looks for densities and calcifications. Densitiescome from invasive carcinomas, fibroadenomas, cysts. Calcifications from secret tori material, necrotic debris. Surrounding dense tissues makes detecting carcinomas harder in mammography. Switch to MRI wave contrast which picks up increased tumor vascularity.

Inflammatory diseases are rare and present withswelling and pain.Acute mastitis happens during lactation, during first month of nursing caused by infection through cracks and fissures and nipples by staphylococcus aureus and streptococci. Staphylococcus tends to make abscesses. Erythema, pain, fever are seen and the infection spreads to entire breast. There may be necrosis and neutrophil infiltration. Treat with antibiotics and drainage of milk.Periductal mastitis does not happen with lactation and is seen in smokers (probably vitamin a deficiency alter ductal epithelium differentiation). Periductal mastitis is seen as a painful erythematosus subareolar mass. The keratinizing squamous epithelium goes in too deep. Keratin gets trapped, causes dilation, and duct rupture. Granulomatous inflammation is followed by secondary infections.Mammary duct ectasia happens in the 40s and 50s and hand is another painful erythematous periareolar mass but this one is not seen with cigarette smoking. There are thick white nipple secretions. The mass is irregular and caused by dilated ducts with lipid laden macrophages. Fibrosis may cause skin and nipple retraction.Fat necrosis is painless masscaused by trauma or surgery. Watch out for domestic violence cause. It consists of hemorrhage early and is then liquefactive necrosis of fat. Fair maybe chalky white or hemorrhagic debris and surrounding macrophages and neutrophils. Later on giant cells,calcifications, and hemosiderin come inand eventually are replaced by scar tissue or an assisted and walled off by collagen.Lymphocytic mastopathy are very hard nodules from college denies stroma due to auto immune disease (type 1 diabetes or thyroid).Granulomatous mastitis is another hypersensitivity reaction that happens after pregnancy due to epithelial changes during lactation.Fibrocystic changes is a diffuse increase in consistency with discrete nodularities. Cysts are a common cause and are solitary, firm, unyielding. All reproductive age breasts have microscopic cysts but are abnormal when larger than 2 mm. These disappear after fine needle aspirations. These lumpy bumpy breasts may be due to cysts, fibrosis, adenosis. Fibrosis is often due to cyst rupture which results in inflammation and scarring. Adenosis is an increase in the number of acini almost as seen in pregnancy.

Epithelial hyperplasia shows epithelia of more than two cell layers which fills and distends the ducts and lobules.Sclerosing adenosis is an increase in number of acini and lobular arrangement is maintained but acini are compressed and distorted. Appearance of solid cords or double strands of cells lying within dense stroma mimics the appearance of invasive carcinoma. Calcifications possible.A radial scar is entrapped glands and hyalinized stroma.

Fibroadenoma is the most common benign breast tumor and happens on their age 30. It is sharply circumscribed and freely movable. Phyllodes tumorhas anaplastic stroma with rapid growth. Usually does not metastasize but if it does will be sarcoma.in a

Hormones:Estrogen develops big ducts.Progesterone develops lobules and acini.Prolactin develops secretory units.Oxytocin contracts myoepithelial cells.