The breasts of an adult woman are milk-producing, tear-shaped glands. They are supported by and attached to the front of the chest wall on either side of the breast bone or sternum by ligaments. They rest on the major chest muscle, the pectoralis major.

The breast has no muscle tissue. A layer of fat surrounds the glands and extends throughout the breast.

The breast is responsive to a complex interplay of hormones that cause the tissue to develop, enlarge and produce milk. The three major hormones affecting the breast are estrogen, progesterone and prolactin, which cause glandular tissue in the breast and the uterus to change during the menstrual cycle.

Each breast contains 15 to 20 lobes arranged in a circular fashion. The fat (subcutaneous adipose tissue) that covers the lobes gives the breast its size and shape. Each lobe is comprised of many lobules, at the end of which are tiny bulb like glands, or sacs, where milk is produced in response to hormonal signals.

Ducts connect the lobes, lobules, and glands in nursing mothers. These ducts deliver milk to openings in the nipple. The areola is the darker-pigmented area around the nipple.

The conic organs which usually give outlet to milk from the mammary glands.

Functionally, the mammary glands produce milk; structurally, they are modified sweat glands. Mammary glands, which are located in the breast overlying the pectoralis major muscles, are present in both sexes, but usually are functional only in the female.

Externally, each breast has a raised nipple, which is surrounded by a circular pigmented area called the areola. The nipples are sensitive to touch, due to the fact that they contain smooth muscle that contracts and causes them to become erect in response to stimulation.

Internally, the adult female breast contains 15 to 20 lobes of glandular tissue that radiate around the nipple. The lobes are separated by connective tissue and adipose. The connective tissue helps support the breast. Some bands of connective tissue, called suspensory (Cooper's) ligaments, extend through the breast from the skin to the underlying muscles. The amount and distribution of the adipose tissue determines the size and shape of the breast. Each lobe consists of lobules that contain the glandular units. A lactiferous duct collects the milk from the lobules within each lobe and carries it to the nipple. Just before the nipple, the lactiferous duct enlarges to form a lactiferous sinus (ampulla), which serves as a reservoir for milk. After the sinus, the duct again narrows and each duct opens independently on the surface of the nipple.

Mammary gland function is regulated by hormones. At puberty, increasing levels of estrogen stimulate the development of glandular tissue in the female breast. Estrogen also causes the breast to increase in size through the accumulation of adipose tissue. Progesterone stimulates the development of the duct system. During pregnancy, these hormones enhance further development of the mammary glands. Prolactin from the anterior pituitary stimulates the production of milk within the glandular tissue, and oxytocin causes the ejection of milk from the glands.

Mammary glands are modified sweat glands. The non-pregnant and non-lactating female breast is composed primarily of adipose and collagenous tissue, with mammary glands making up a very minor proportion of breast volume. The mammary gland is composed of milk-transporting lactiferous ducts, which expand and branch extensively during pregnancy in response to estrogen, growth hormone, cortisol, and prolactin. Moreover, in response to progesterone, clusters of breast alveoli bud from the ducts and expand outward toward the chest wall. Breast alveoli are balloon-like structures lined with milk-secreting cuboidal cells, or lactocytes, that are surrounded by a net of contractile myoepithelial cells. Milk is secreted from the lactocytes, fills the alveoli, and is squeezed into the ducts. Clusters of alveoli that drain to a common duct are called lobules; the lactating female has 12–20 lobules organized radially around the nipple. Milk drains from lactiferous ducts into lactiferous sinuses that meet at 4 to 18 perforations in the nipple, called nipple pores. The small bumps of the areola (the darkened skin around the nipple) are called Montgomery glands. They secrete oil to cleanse the nipple opening and prevent chapping and cracking of the nipple during breastfeeding.

The Process of Lactation

The pituitary hormone prolactin is instrumental in the establishment and maintenance of breast milk supply. It also is important for the mobilization of maternal micronutrients for breast milk.

Near the fifth week of pregnancy, the level of circulating prolactin begins to increase, eventually rising to approximately 10–20 times the pre-pregnancy concentration. We noted earlier that, during pregnancy, prolactin and other hormones prepare the breasts anatomically for the secretion of milk. The level of prolactin plateaus in late pregnancy, at a level high enough to initiate milk production. However, estrogen, progesterone, and other placental hormones inhibit prolactin-mediated milk synthesis during pregnancy. It is not until the placenta is expelled that this inhibition is lifted and milk production commences.

After childbirth, the baseline prolactin level drops sharply, but it is restored for a 1-hour spike during each feeding to stimulate the production of milk for the next feeding. With each prolactin spike, estrogen and progesterone also increase slightly.

When the infant suckles, sensory nerve fibers in the areola trigger a neuroendocrine reflex that results in milk secretion from lactocytes into the alveoli. The posterior pituitary releases oxytocin, which stimulates myoepithelial cells to squeeze milk from the alveoli so it can drain into the lactiferous ducts, collect in the lactiferous sinuses, and discharge through the nipple pores. It takes less than 1 minute from the time when an infant begins suckling (the latent period) until milk is secreted (the let-down). Figure 28.23 summarizes the positive feedback loop of the let-down reflex.

Figure 28.23 Let-Down Reflex A positive feedback loop ensures continued milk production as long as the infant continues to breastfeed.

The prolactin-mediated synthesis of milk changes with time. Frequent milk removal by breastfeeding (or pumping) will maintain high circulating prolactin levels for several months. However, even with continued breastfeeding, baseline prolactin will decrease over time to its pre-pregnancy level. In addition to prolactin and oxytocin, growth hormone, cortisol, parathyroid hormone, and insulin contribute to lactation, in part by facilitating the transport of maternal amino acids, fatty acids, glucose, and calcium to breast milk.

What Are Breasts?

Breasts are complex, specialized organs whose primary function is to produce milk for the infant and baby. They are made up mainly of fat and breast tissue, intermingled with nerves, blood vessels, lymph vessels and lymph nodes, muscle tissue, and connective tissue.

Breast tissue extends from the breastbone to the underarm, and from below the collarbone to the level of the sixth or seventh rib. Breast tissue is composed of lobules, lobes, and mammary ducts. Fifteen to twenty lobes are arranged beneath the nipple and areola (the shaded area around the nipple), like petals on a flower. Each lobe contains thousands of tiny round sacs called lobules, and lobules hold the bulbs that produce breast milk. A single breast contains up to a million lobules. The lobules are connected to the mammary ducts like bunches of grapes on stems. Mammary ducts are the canals that carry breast milk to the nipple openings. Fat covers the breast tissue and gives the breast its shape.

Lymphatic System

The breast contains lymph vessels that drain into a network of lymph nodes located around the edges of the breast, in the underarm (axilla), and near the collarbone. These lymph nodes are embedded in fat, which makes it difficult to remove them. Underarm lymph nodes are often the first place breast cancer spreads.

Blood Vessels

Several arteries supply the breasts with blood: the internal mammary, axillary, and intercostal (between the ribs) arteries. The internal mammary, axillary, and intercostal veins carry blood away from the breasts. The breast's surface veins carry blood to these veins and to the lungs. Cancerous cells may travel through the surface veins to the lungs, where they may form tumors. The intercostal veins run to the spine, allowing cancerous cells in the breast to spread to bone tissue.

Muscles

The chest muscles are overlaid by a fibrous covering. They are located under the breasts and include the following:

• Major and minor pectorals. The main chest muscles, which lie directly behind the breast, in front of the ribs. They attach to the collarbone, the breastbone, the humerous (upper arm) bone, the shoulder joint, and the third, fourth, and fifth ribs and the muscles between those ribs.

• Serratus magnus. Attaches to the first eight or nine ribs and rib muscles and connects with the shoulder blades in the back.

• Rectus abdominus. Extends from the pubic bone and attaches to the cartilage of the fifth, sixth, and seventh ribs.

Nerves

The skin of the upper breast is innervated (supplied with nerves) that branch off from nerves in the neck. The skin of the lower breast is innervated with nerves that extend from the spine and between the ribs. The thoracic nerve crosses over the underarm lymph nodes and helps to move the upper arm. Surgeons have to be careful not to injure this nerve when operating near the underarm.

Connective Tissue

Fascia (fibrous connective tissue) separates the breast tissue from the skin and also from the chest muscles. Ligaments run from the deep fascia throughout the breast tissue and attach to the dermis (the second layer of skin). Connective tissue helps hold all the components of the breast in place.

Changes During Pregnancy and Birth

The function of the breast is to produce milk and colostrum for the infant. The breast undergoes many important changes when a woman becomes pregnant, in preparation for producing milk. Estrogen and progesterone stimulate cell growth and development of the breast. Special hormones called prolactin and somatomammotrophin, produced during pregnancy, also play a role. The cells in the glands of the breast tissue change shape, become bigger, and increase in number. Later on in the pregnancy, the lobules start to produce milk, which begins to accumulate in the ducts. Muscle tissue around the lobules helps to squeeze the milk into the ducts.

During breastfeeding, glands on the areola secrete a fluid to lubricate the nipple, and muscles in the nipple allow it to become erect. A protein and antibody-rich fluid called colostrum is produced during the last weeks of pregnancy and during the first few episodes of nursing.

Breast Density

Radiologists grade breasts on the basis of how dense they are. Dense breasts have a high proportion of ductal and connective tissue, while less-dense breasts have a higher proportion of fatty tissue. The four commonly used categories are: (1) entirely fat, (2) scattered fibroglandular densities, (3) heterogeneously dense, and (4) extremely dense. Women with dense breasts have a higher risk of developing breast cancer.

How Breast Anatomy Changes

Everyone, male and female, is born with a small amount of breast tissue, but only the presence of certain hormones, particularly estrogen and progesterone, can stimulate the development of that tissue into breasts. In girls, the small patch of breast tissue in each breast lies dormant until puberty. At puberty, hormones stimulate the breast tissue to grow and form the mature system of lobules and ducts. Breast tissue remains inactive until pregnancy, when the lobules begin to multiply and produce milk.

In menopause, hormone production slows. The number of lobules in the breast decreases and the ones that remain shrink in size. Breast density diminishes, and a larger proportion of the breast is made up of fat than in younger women.

Removal and examination of the sentinel node(s) (the first lymph node(s) to which cancer cells are likely to spread from a primary tumor). To identify the sentinel lymph node(s), the surgeon injects a radioactive substance, blue dye, or both near the tumor. The surgeon then uses a probe to find the sentinel lymph node(s) containing the radioactive substance or looks for the lymph node(s) stained with dye. The surgeon then removes the sentinel node(s) to check for the presence of cancer cells.

What is cancer?

The process of cell growth in the body is normally an orderly one. Cells grow and divide as necessary to produce more cells as they are needed. Cells that are old or damaged die, and are replaced with new cells.

In cancer, something has gone wrong with this process. The cell's DNA has been damaged. DNA is a substance found in every cell in the body that directs the cell's functioning and reproduction. Cell DNA may be damaged by environmental agents, such as radiation (including excessive sunlight), viruses, chemicals, and tobacco smoke. Cells with damaged DNA may also be inherited from one's parents.

Normally, if a cell has damaged DNA, it either repairs it or dies. But in cancer, the damaged cell starts to reproduce in an uncontrolled way, creating more abnormal cells. It outlives the normal cells around it and forms a tumor (a lump or mass).

Not all tumors are invasive. Benign tumors may simply be removed and are unlikely to grow back again. Malignant tumors, however, are cancerous, and they may start to invade surrounding tissues. By entering the bloodstream or the lymph system, cancer cells can spread throughout the body.

Types of cancer

Cancer is not one disease. There are more than one hundred different types of cancer, and they all behave differently. Liver cancer, for instance, grows at a different rate than colorectal cancer, and responds to different treatments.

Cancer is named after the site where it originates, no matter where it spreads. Breast cancer that has spread to the lungs is termed metastatic breast cancer, not lung cancer. Although there are many different types of cancer, they can all be divided into five main categories:

• Carcinoma. Cancer that begins in epithelial cells (cells that form the skin or tissues that line or cover internal organs)
• Sarcoma. Cancer that begins in connective tissue (such as bone, cartilage, fat, muscle, and blood vessels)
• Leukemia. Cancer that starts in blood-forming tissue (like bone marrow)
• Lymphoma and myeloma. Cancers that begin in the cells of the immune system
• Central nervous system cancers. Cancers that begin in the tissues of the brain or spinal cord

Cancers of the breast

Most breast cancers are carcinomas, meaning they arise in the epithelial cells lining the ducts or the lobules. Cancers may begin in nonepithelial parts of the breast, such as the blood vessels or the connective tissue, but they are much less common than epithelial cancers.

The majority (80-85%) of breast cancers arise in the cells lining the mammary ducts. This type of cancer is called ductal carcinoma. Most of the remaining cases of breast cancer arise in the cells lining the lobules, termed lobular carcinoma. Medullary, mucinous, and tubular carcinomas are rare forms of breast cancer.

In Situ and Invasive Cancer

Breast cancers are classified as in situ or invasive (sometimes called infiltrating).

• Carcinoma in situ occurs when cancer cells grow inside ducts or lobules but don't invade adjacent fatty tissues. ("In situ" is Latin for "in place.")
• Invasive carcinomas break out of the ducts or lobules and penetrate surrounding tissue. This gives the cancer the opportunity to metastasize (spread) by entering the lymphatic system or blood vessels and travelling to other organs or bone tissue.

Types of Breast Cancer:

Ductal Carcinoma

• Ductal Carcinoma In Situ (DCIS). DCIS is cancer than remains confined with the mammary ducts and is the most commonly diagnosed noninvasive breast cancer. It is sometimes referred to as a precancerous condition, as it may be a precursor to invasive ductal carcinoma. There are often no symptoms. If DCIS remains confined, it is easily treated. Treatment is usually lumpectomy, possibly followed by radiation and sometimes chemotherapy.
• Invasive (infiltrating) ductal carcinoma (IDC). IDC begins in a mammary duct, breaks through the wall of the duct, and penetrates into the surrounding fatty tissue of the breast. This is the most common type of invasive breast cancer: about 80-85% of invasive breast cancers are IDCs. IDC may metastasize to other parts of the body.

Lobular Carcinoma

• Lobular carcinoma in situ (LCIS). LCIS is a noninvasive cancer that begins in the lobules. It does not break through the lobular walls, but may be a precursor to invasive lobular carcinoma. LCIS is usually treated by lumpectomy, sometimes followed with radiation.
• Invasive lobular carcinoma (ILC). ILC is an invasive cancer that begins in the breast's milk-producing glands (lobules). It's often harder to detect ILC by mammogram than IDC. About 10% of invasive breast cancers are ILCs. Like IDC, it can spread to other parts of the body.

Inflammatory Carcinoma

• Inflammatory carcinoma an uncommon (1-3%) but aggressive form of breast cancer. It may start under the skin in the soft tissues of the breast, or it may arise in the skin itself. It can cause the skin to have an orange peel appearance (peau d' orange) and become reddened. Unlike ductal and lobular cancers, it is treated first with chemotherapy and then with surgery.

Medullary Carcinoma

• Medullary carcinoma is an invasive cancer with special features that distinguish it from other forms of breast cancer. It forms a well-defined boundary between tumor tissue and normal tissue, its cells are unusually large, and immune system cells are present at the edges of the tumor. About 3-5% of invasive breast cancers are medullary carcinomas. The prognosis (outlook) for medullary carcinomas is usually better than for the more common types of invasive breast cancer.

Tubular Carcinoma

• Tubular carcinoma is a type of invasive ductal breast carcinoma. It is called tubular because the cells, when viewed under a microscope, resemble small tubes. About 2% of all invasive breast cancers are tubular carcinomas. They generally have a better prognosis than the more common invasive breast carcinomas.

Paget's Disease of the Nipple/Areola

• This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple and then to the areola. It's almost always associated with DCIS or IDC. The skin of the nipple and areola often appears crusted, scaly, and red, with areas of bleeding or oozing. It is rare, accounting for only about 1% of all cases of breast cancer. It is usually treated with mastectomy.

Mucinous (Colloid) Carcinoma

• A rare type of invasive breast cancer formed by mucus-producing cancer cells. The prognosis for this type of breast cancer is generally better than for the more common types of invasive breast cancer.

Risk Factors

A risk factor is anything that increases the chances of getting a disease. No one knows exactly what causes breast cancer, and why some people with few risk factors may develop the disease, and other people with many risk factors may not. Some risk factors are controllable, some aren't. Although there is not 100% sure way of preventing breast cancer, it is possible to reduce your chances of getting breast cancer by reducing or eliminating the risk factors that you can control.

Risk Factors You Can't Control

• Gender. Women have a 100-times greater chance of developing breast cancer than men.
• Age. Almost 80% of breast cancers occur in women over age 50.
• Genetics. About 5-10% of breast cancers are thought to be hereditary and due to gene mutations (changes) inherited from a parent. The most common inherited mutations are those of the BRCA1 and BRCA2 genes. o Family history of breast cancer. Having a mother, sister, or daughter with breast cancer doubles a woman's risk.
• Personal history of breast cancer. Having had breast cancer triples or quadruples the chances of developing another tumor. (This is different from recurrence.)
• Race. In the US, white women have the highest chance of developing breast cancer, while African-American women have a greater chance of dying from it. Asian, Hispanic, and Native-American women have a lower risk of developing and dying from breast cancer. o Dense breasts. Women with dense breast tissue (tissue that has more glandular than fatty tissue) have a higher risk of breast cancer.
• Early or late menstruation. Women who began their periods early (before age 12) or who had a late menopause (after age 55) have a slightly greater risk of breast cancer. This may be because these women have a greater number of menstrual periods during their lifetimes.
• Previous chest radiation. Having had chest radiation for a different condition (eg, Hodgkin's disease) significantly increases risk of breast cancer.
• DES exposure. Women who took diethylstilbestrol (DES) during pregnancy, and women whose mothers took it during pregnancy, may have a slightly higher risk of breast cancer.

Risk Factors You Can Control

• Alcohol. Women who have one alcoholic drink a day have a very small increase in risk. Women who have 2-5 drinks daily have about 1.5 times the risk of women who drink no alcohol.
• Children. Not having children, or having a first child after age 30, slightly increases breast cancer risk.
• Recent oral contraceptive use. Use of oral contraceptives slightly increases risk, but risk declines once their use is stopped.
• Hormone therapy. Long-term use of combination hormone-replacement therapy for the relief of symptoms of menopause increases breast cancer risk.
• Not breastfeeding. Breastfeeding may lower breast cancer risk, especially if done for a long period of time. This may be because doing so reduces the number of menstrual periods a woman has during her lifetime.
• Overweight or obesity. Being overweight or obese increases breast cancer risk, especially after menopause.
• Lack of physical activity. Being inactive increases the risk of breast cancer. As little as 1