A

BREAST

Anatomy and physiology

The human breasts are paired organs lying on the anterior chest, extending from the second to the sixth ribs. The breasts in other animals are usually multiple and extend on to the abdomen, which explains the rare anomaly of multiple paired breasts that occasionally occurs in humans. The breasts are thought to be modified sweat glands, and therefore lie in the subcutaneous fat in front of the pectoral (chest) muscles. The breast has a central nipple through which the fifteen to twenty milk ducts exit; the nipple is usually protuberant, but can be inverted in some women.

The breast develops in young girls at around the age of ten or eleven due to the increasing release of pituitary hormones in puberty. The gland grows into the normal conical or rounded adult shape by around sixteen years of age, but swells considerably in pregnancy when milk production occurs. During the normal menstrual cycle, many women experience breast tenderness and swelling during the seven to ten days prior to menstruation.

Changes with aging

As a woman ages, the glandular component is replaced by fat, and the breast becomes softer and hangs lower as the suspensory ligaments inside the breast stretch. As the breast ages, the milk-producing sacs (lobules) may dilate with fluid and lead to the information of breast cysts, which sometimes enlarge sufficiently to be felt as lumps. The increase in fat content makes the older breast more lucent to X rays and easier to compress, so the clarity of a mammographic picture is greater in the older woman, making a small tumor more visible. This fact explains the greater accuracy of mammograms in older women and the adoption of population mammographic screening in women over forty-five years of age. As the breast ages, the skin gets thinner and the breast consists mainly of soft fat, making the breast more liable to bruising or trauma.

Estrogen replacement therapy (ERT), used to control hot flashes, tends to oppose the reduction of density that occurs with age and can produce tenderness, swelling, and lumpiness in the breast, manifestations normally seen in younger women. Thus, women on ERT may find their breast to be tender and fuller while on therapy. Surveys of ERT have shown a slight increase in breast cancer risk after more than fifteen years of estrogen use, but this problem is balanced by the improved quality of life on the therapy. Studies do not seem to indicate any major increase in the risk for breast cancer from ERT in women with a family history.

Breast diseases

As the breast ages, some diseases become more common. Breast cysts occur in about 7 percent of women and are usually seen between the ages of forty and sixty. These are easily treated by aspiration of the cyst fluid, which may be facilitated using ultrasound guidance. The breast gradually becomes less lumpy after menopause, as the fall in estrogen levels causes shrinkage of the gland tissue, with a relative increase in the fat content. Eventually, the breast becomes pendulous, a change that tends to be accelerated in heavier, fuller breasts. Oversize and pendulous breasts can be corrected by a surgical reduction mammoplasty, or by a simple "hitch up" operation if no tissue needs to be removed.

Breast cancer is the most common malignancy in females, and the lifetime risk is roughly one in ten. Breast cancer is strongly associated with age; it is uncommon below thirty years of age, but common after the age of forty-five. The cancer usually originates from faulty cell division in the breast lobules, and it may initially commence as a noninvading type of cancer whereby malignant cells line the ducts within the breast (intraductal noninvasive cancer—also know as ductal carcinoma in situ, or DCIS). Invasive cancer occurs when the malignant cells acquire the ability to break through the duct walls and invade into the surrounding breast tissue. Further spread can occur via the blood vessels or lymphatic channels, which can also become invaded by cancer cells. These cells can then travel via the bloodstream to the bones, brain, lungs, or liver. Lumps that may indicate breast cancer can be detected by self-examination, mammography, and ultrasound, and tumors as small as four or five millimeters can be seen by these techniques. Once detected by these methods, a needle can be used to obtain a biopsy of either cells or tissue to make a diagnosis. Current therapy may involve surgical removal of the lump (lumpectomy) or the breast (mastectomy), followed by chemotherapy, radiotherapy, and hormone therapy. Different combinations may be used, depending on the individual patient or tumor, but hormonal therapies are used more often in older women.

When tumors are found to be large on initial diagnosis, chemotherapy and/or radiation therapy may be given before surgery. The results of therapy have been improving, and mortality from breast cancer is falling in most developed countries due to better combinations of therapy, as well as a reduction in tumor size due to mammographic screening. Around 85 percent of women with a smaller cancer of less then one inch (2.5 cms) with no nodal spread can expect to survive ten years after modern therapy.

Despite these modern therapies, many women still die from breast cancer, and prevention of breast cancer may be the preferred way to reduce deaths. Studies in the United States have shown a substantial reduction in breast cancer in high-risk women taking the antiestrogen drug tamoxifen for two years. Current studies are exploring other hormone interventions in women at high risk of breast cancer.

R. E. MANSEL