Breast cancer is a potentially dangerous tumor that develops in the cells of the breast. Cancer cells can spread from the breast to other parts of the body.
In the United States, breast cancer is a very common cancer among women; only skin cancer is more common. About 246,000 cases of invasive breast cancer in women were diagnosed in the United States in 2015. Breast cancer may occur in men, too, but is much rarer; there are about 2,350 cases of breast cancer in men diagnosed in the United States each year. Breast cancer is also the second-leading cause of cancer death in women, behind lung cancer. However, deaths from breast cancer were reduced substantially in the late 1990s and into the next decade because more effective treatments became available, and because skilled health professionals using state-of-the-art equipment were able to find these cancers earlier, when they are easier to treat. Since 2005 the incidence of breast cancer has remained level among women in the United States, while deaths from breast cancer have declined.
A woman's breast contains millions of milk-producing glands called lobules (LOB-yools) that look like tiny bunches of grapes. When a woman is lactating after giving birth, milk from the lobules flows outward through channels or ducts to the nipple. Breast cancer begins when a single cell in a duct or lobule undergoes changes (mutations) that cause it to start growing out of control. At first, the cells remain within the duct or lobule despite their prolific growth. At this stage, the cancer is called cancer in situ, meaning that the cancer is still confined to the location or site where it started. Later, the cells may break out of the duct or lobule into the fat and surrounding tissue, where they continue to divide and multiply. The cells form a mass called a tumor that sends out signals in the form of proteins to prompt new blood vessels to form. These vessels provide the nourishment a tumor requires to continue growing.
Cancer cells may enter the bloodstream, where the body's immune system (the body's defense against disease) may kill them. If the immune system is not successful, the cancer cells may travel to distant organs of the body, settle there, grow, and divide. This spreading process is called metastasis (me-TAS-tuh-sis). Breast cancer cells are most likely to spread to the lungs, liver, and bones.
Breast cancer is not contagious nor is it caused by an injury to the breast. There are certain risk factors, including smoking and obesity * , that may increase the chance of getting breast cancer. As of 2016, exactly how some of these risk factors cause cells to become cancerous was not known.
Breast cancer in teenagers is very rare; one published report gives a figure of 1.3 cases of breast cancer per million teenage girls. A girl whose breasts are developing may feel some discomfort from time to time, but this pain is a normal part of the body's functioning and is not a sign of cancer.
A woman whose mother, sister, or daughter has had breast cancer has twice the risk of getting the disease compared to a woman without the family history of breast cancer. Most women diagnosed with breast cancer, however, do not have such a family history.
Women who inherit certain mutated genes * are at higher risk of getting breast cancer. Two of the genes commonly implicated in this increased risk are BRCA1 and BRCA2 (BRCA is an initialism for BReast CAncer; many gene names are abbreviations of the name of a disorder or a protein involved in a disorder). Each person inherits two copies of any given gene from his or her parents, one from the mother and one from the father. When only one copy of a gene is required to have an effect, it is known as an autosomal (aw-toe-SO-mal) dominant gene. BRCA1 and BRCA2, as well as some genes associated with other cancers, are autosomal dominant genes. According to the National Cancer Institute, the presence of BRCA1 or BRCA2 genes can increase breast cancer risk by three to seven times. Although these two mutations account for no more than 10 percent of the overall number of breast cancer cases, women should learn whether they have a family history of the disease and report it to their health professionals.
Researchers suspect that natural substances in the body called hormones, especially the female hormone estrogen, play a role in promoting some types of breast cancer. Numerous research studies have linked a high lifetime level of exposure to estrogen to an increased risk of breast cancer. Estrogen levels may become elevated due to obesity, use of birth control pills or other estrogen-containing medications, exposure to environmental chemicals, and other causes.
Older women have a higher risk of developing breast cancer; 95 percent of new cases occur in women over the age of 40. The median age of women in the United States diagnosed with breast cancer is 61. Another risk factor is early age for a girl's first menstrual period as well as late age for the onset of menopause. Women who have their first child after the age of 30, or who do not have any children, also have a slightly higher risk. In addition, a woman who has already had breast cancer diagnosed in one breast is at higher risk of getting it in the other breast.
The first sign of breast cancer is often a painless lump in the breast. In some cases, the shape, color, or texture of the breast or nipple may be different; or the nipple may be tender or have a discharge. Sometimes, medical professionals may find the cancer before symptoms occur. One method for doing so is the routine or screening mammography (mam-MOG-ra-fee) (x-ray examination of the breasts). A mammogram may show changes that indicate a possibility of cancer, and medical professionals will then run other tests to check further for evidence of the disease.
If a screening mammogram or a woman's symptoms suggest cancer, her doctor will request a biopsy * . In this procedure, a small amount of tissue is removed from the abnormal area of the breast and examined under a microscope. Most biopsies show that the tissue is benign, which means that the tissue is free of cancer, and the woman may need no further treatment. A woman who receives a diagnosis of cancer, however, should proceed to learn about the disease and discuss her options for treatment with her health professionals, as well as her friends and family.
Breast cancers that do not appear to have spread may be treated through a lumpectomy (lump-EK-to-mee), a procedure in which the surgeon removes only the tumor. Sometimes, however, a mastectomy (mas-TEK-to-mee) may be required, which is the surgical removal of the entire breast. The size and sometimes the type of tumor will determine which is best.
Follow-up treatment may include radiation therapy and anticancer medication, called chemotherapy * , to kill any remaining cancer cells and to prevent them from returning. The choice of follow-up treatment depends on the kind of tumor and whether it appears to have spread to the lymph nodes * or other parts of the body.
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National Cancer Institute. “What You Need to Know about Breast Cancer.” http://www.cancer.gov/cancertopics/wyntk/breast (accessed April 12, 2016).
American Cancer Society. 250 Williams St. NW, Atlanta, GA 303031034. Toll-free: 800-227-2345. Website: http://www.cancer.org (accessed April 12, 2016).
Breast Cancer and the Environment Research Program. Website: http://www.bcerc.org (accessed April 12, 2016).
National Cancer Institute. BG 9609 MSC 9760, 9609 Medical Center Dr., Bethesda, MD 20892-9760 Toll-free: 800-422-6237. Website: http://www.cancer.gov (accessed April 12, 2016).
* obesity (o-BEE-si-tee) is an excess of body fat. People are considered obese if they weigh more than 30 percent above what is healthy for their height.
* genes (JEENS) are chemical structures composed of deoxyribonucleic acid (DNA) that help determine a person's body structure and physical characteristics. Inherited from a person's parents, genes are contained in the chromosomes found in the body's cells.
* biopsy (BI-op-see) is a test in which a small sample of skin or other body tissue is removed and examined for signs of disease.
* chemotherapy (KEE-mo-THER-apee) is the treatment of cancer with powerful drugs that kill cancer cells.
* lymph nodes (LIMF) are small bean-shaped masses of tissue containing immune system cells that fight harmful microorganisms. Lymph nodes may swell during infections.