Breast

The breast is one of two prominences found on the upper ventral region of the torso of female and male primates. In females, it serves as the mammary gland, which produces and secretes milk and feeds infants. Both females and males develop breasts from the same embryological tissues. At puberty, estrogens, in conjunction with growth hormone, cause breast development. Males do not develop pronounced or physiologically matured breasts because their bodies produce lower levels of estrogens and higher levels of androgens, namely testosterone, which suppress the effects of estrogens in developing breast tissue. The breasts of females are typically far more prominent than those of males.

Subcutaneous fat covers and envelops a network of ducts that converge to the nipple, and these tissues give the breast its size and shape. At the ends of the ducts are lobules, or clusters of alveoli, where milk is produced and stored in response to hormonal signals. During pregnancy, the breast responds to a complex interaction of hormones, including estrogens, progesterone, and prolactin, that mediate the completion of its development, namely lobuloalveolar maturation, in preparation of lactation and breastfeeding. Upon childbirth, the alveoli are stimulated to produce and secrete milk for infants.

Breast milk

Breast milk is the milk produced by the breasts (or mammary glands) of a human female for her infant offspring. Milk is the primary source of nutrition for newborns before they are able to eat and digest other foods; older infants and toddlers may continue to be breastfed, either exclusively or in combination with other foods from around six months of age when solid foods may be introduced.

Benefits

The baby nursing from his or her own mother is the most common way of obtaining breast milk, but the milk can be pumped and then fed by baby bottle, cup and/or spoon, supplementation drip system, or nasogastric tube. Breast milk can be supplied by a woman other than the baby's mother, either via donated pumped milk (generally from a milk bank or via informal milk donation), or when a woman nurses a child other than her own at her breast, a practice known as wetnursing.

The World Health Organization recommends exclusive breastfeeding for the first six months of life, with solids gradually being introduced around this age when signs of readiness are shown. Supplemented breastfeeding is recommended until at least age two and then for as long as the mother and child wish. Breastfeeding offers health benefits to mother and child even after toddlerhood. These benefits include a 73% decreased risk of sudden infant death syndrome, increased intelligence, decreased likelihood of contracting middle ear infections, cold and flu resistance, a tiny decrease in the risk of childhood leukemia, lower risk of childhood onset diabetes, decreased risk of asthma and eczema, decreased dental problems, decreased risk of obesity later in life, and a decreased risk of developing psychological disorders, including in adopted children.

Breast cancer

Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, or a red scaly patch of skin. In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.

Risk factors for developing breast cancer include: female sex, obesity, lack of physical exercise, drinking alcohol, hormone replacement therapy during menopause, ionizing radiation, early age at first menstruation, having children late or not at all, older age, and family history. About 5–10% of cases are due to genes inherited from a person's parents, including BRCA1 and BRCA2 among others. Breast cancer most commonly develops in cells from the lining of milk ducts and the lobules that supply the ducts with milk. Cancers developing from the ducts are known as ductal carcinomas, while those developing from lobules are known as lobular carcinomas. In addition, there are more than 18 other sub-types of breast cancer. Some cancers develop from pre-invasive lesions such as ductal carcinoma in situ. The diagnosis of breast cancer is confirmed by taking a biopsy of the concerning lump. Once the diagnosis is made, further tests are done to determine if the cancer has spread beyond the breast and which treatments it may respond to.