Other than skin cancer, breast cancer is the most common type of cancer among women in the United States. More than 180,000 women are diagnosed with breast cancer each year. The National Cancer Institute (NCI) has written this fact sheet to help patients with breast cancer and their families and friends better understand this disease. We hope others will read it as well to learn more about breast cancer.
This fact sheet discusses screening and early detection, symptoms, diagnosis, treatment, and rehabilitation. It also has information to help patients cope with breast cancer.
Male breast cancer
Breast cancer affects more than 1,000 men in this country each year. Although this fact sheet was written mainly for women, much of the information on symptoms, diagnosis, treatment, and living with the disease applies to men as well. However, the “Detecting Breast Cancer” section does not apply to men. Experts do not recommend routine screening for men.
Research has led to progress against breast cancer–better treatments, a lower chance of death from the disease, and improved quality of life. Through research, knowledge about breast cancer keeps increasing. Scientists are learning more about what causes breast cancer and are exploring new ways to prevent, detect, diagnose, and treat this disease.
The Cancer Information Service at 800-4-CANCER and other NCI resources listed under “National Cancer Institute Information Resources” can provide the latest, most accurate information on breast cancer. Publications listed in the “National Cancer Institute Booklets” section are available from the Cancer Information Service. Also, many NCI publications may be viewed or ordered on the Internet at http://cancer.gov/publications.
The breasts
Each breast has 15 to 20 sections called lobes. Within each lobe are many smaller lobules. Lobules end in dozens of tiny bulbs that can produce milk. The lobes, lobules, and bulbs are all linked by thin tubes called ducts. These ducts lead to the nipple in the center of a dark area of skin called the areola. Fat surrounds the lobules and ducts. There are no muscles in the breast, but muscles lie under each breast and cover the ribs.
Each breast also contains blood vessels and lymph vessels. The lymph vessels carry colorless fluid called lymph, and lead to small bean-shaped organs called lymph nodes. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the chest. Lymph nodes are also found in many other parts of the body.
Understanding the cancer process
Cancer is a group of many related diseases that begin in cells, the body’s basic unit of life. To understand cancer, it is helpful to know what happens when normal cells become cancerous.
The body is made up of many types of cells. Normally, cells grow and divide to produce more cells only when the body needs them. This orderly process helps keep the body healthy. Sometimes, however, cells keep dividing when new cells are not needed. These extra cells form a mass of tissue, called a growth or tumor. Tumors can be benign or malignant.
Benign tumors are not cancer. They can usually be removed, and in most cases, they do not come back. Cells from benign tumors do not spread to other parts of the body. Most important, benign breast tumors are not a threat to life.
Malignant tumors are cancer. Cells in these tumors are abnormal. They divide without control or order, and they can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the bloodstream or the lymphatic system. That is how cancer spreads from the original (primary) cancer site to form new tumors in other organs. The spread of cancer is called metastasis.
When cancer arises in breast tissue and spreads (metastasizes) outside the breast, cancer cells are often found in the lymph nodes under the arm (axillary lymph nodes). If the cancer has reached these nodes, it means that cancer cells may have spread to other parts of the body–other lymph nodes and other organs, such as the bones, liver, or lungs. When cancer spreads from its original location to another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if breast cancer spreads to the brain, the cancer cells in the brain are actually breast cancer cells. The disease is called metastatic breast cancer. (It is not brain cancer.) Doctors sometimes call this “distant” disease.
This booklet deals with breast cancer. For information about benign breast lumps and other benign breast changes, read NCI’s booklet, “Understanding Breast Changes: A Health Guide for All Women.”
Breast cancer: Who’s at risk?
The exact causes of breast cancer are not known. However, studies show that the risk of breast cancer increases as a woman gets older. This disease is very uncommon in women under the age of 35. Most breast cancers occur in women over the age of 50, and the risk is especially high for women over age 60. Also, breast cancer occurs more often in white women than African American or Asian women.
Research has shown that the following conditions increase a woman’s chances of getting breast cancer:
Personal history of breast cancer. Women who have had breast cancer face an increased risk of getting breast cancer in their other breast.
Family history. A woman’s risk for developing breast cancer increases if her mother, sister, or daughter had breast cancer, especially at a young age.
Certain breast changes. Having a diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase a woman’s risk for developing cancer.
Genetic alterations. Changes in certain genes (BRCA1, BRCA2, and others) increase the risk of breast cancer. In families in which many women have had the disease, gene testing can sometimes show the presence of specific genetic changes that increase the risk of breast cancer. Doctors may suggest ways to try to delay or prevent breast cancer, or to improve the detection of this disease in women who have these changes in their genes.
Other factors associated with an increased risk for breast cancer include:
Estrogen. Evidence suggests that the longer a woman is exposed to estrogen (estrogen made by the body, taken as a drug, or delivered by a patch), the more likely she is to develop breast cancer. For example, the risk is somewhat increased among women who began menstruation at an early age (before age 12), experienced menopause late (after age 55), never had children, or took hormone replacement therapy for long periods of time. Each of these factors increases the amount of time a woman’s body is exposed to estrogen.
DES (diethylstilbestrol) is a synthetic form of estrogen that was used between the early 1940s and 1971. Women who took DES during pregnancy to prevent certain complications are at a slightly higher risk for breast cancer. This does not appear to be the case for their daughters who were exposed to DES before birth. However, more studies are needed as these daughters enter the age range when breast cancer is more common.
Late childbearing. Women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.
Breast density. Breasts that have a high proportion of lobular and ductal tissue appear dense on mammograms. Breast cancers nearly always develop in lobular or ductal tissue (not fatty tissue). That’s why cancer is more likely to occur in breasts that have a lot of lobular and ductal tissue (that is, dense tissue) than in breasts with a lot of fatty tissue. In addition, when breasts are dense, it is more difficult for doctors to see abnormal areas on a mammogram.
Radiation therapy. Women whose breasts were exposed to radiation during radiation therapy before age 30, especially those who were treated with radiation for Hodgkin’s disease, are at an increased risk for developing breast cancer. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.
Alcohol. Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol.
Most women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older. Scientists are conducting research into the causes of breast cancer to learn more about risk factors and ways of preventing this disease.
