Breast Cancer

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.

How Common Is Breast Cancer?

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.

Anatomy of the female breast. Ducts carry milk from the lobules to the nipple. The lobules and ducts are surrounded by fatty tissue and ligaments called stroma.

Anatomy of the female breast. Ducts carry milk from the lobules to the nipple. The lobules and ducts are surrounded by fatty tissue and ligaments called stroma.
Illustration by Frank Forney. © 2016 Cengage Learning®.

How Does Breast Cancer Start?

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.

How Common Is Breast Cancer?

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.

Women, Breast Cancer, and Mammograms
Breast Cancer in Teenagers

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.

Family History

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.

BRCA1, BRCA2, and Estrogen

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.

Diet and Lifestyle
Men and Breast Cancer

How Do Doctors Diagnose and Treat Breast Cancer?


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.

Can Breast Cancer Be Prevented?

Support groups

For women with breast cancer, talking to other women who are living with the disease can be a very comforting experience. For women whose breast cancer has come back or spread, support can be even more beneficial. One study showed that women with metastatic breast cancer who participated in support groups lived an average of almost two years longer than women who did not.

Women who have just been diagnosed with breast cancer also may find it helpful to meet and to talk to women who had breast cancer 10 or 15 years earlier and who are now living happy, healthy lives.

Listings of support groups are available through many organizations, including the American Cancer Society.

The history of breast cancer and its treatment goes back thousands of years.

Will Breast Cancer Ever Be Preventable?

Besides focusing on ongoing studies to improve chemotherapy options for treating breast cancer, many researchers were working in the early 21st century on genetic tests to determine who is more susceptible to the disease. These tests, which began with a simple blood sample, searched for mutated genes that may make a woman more likely to develop breast cancer. While the tests did not identify whether a woman definitely would or would not get breast cancer, they showed the presence of such mutated genes as BRCA1 or BRCA2, which are related to breast cancer. Numerous studies were under way as of 2016 to investigate how best to use the information from such genetic tests to help a woman lower her risk of developing breast cancer.

Tamoxifen Research

Patient being assisted by a technician during a mammography.

Patient being assisted by a technician during a mammography.
Tyler Olson/
Helping Women with Cancer Look Their Best

Look Good Feel Better (LGFB) is a different type of cancer support group in which women (and teens) with any type of cancer get together to have beauty makeovers and try out cosmetics and hair styles to help manage the effects of cancer treatment on their appearance. Beauty professionals certified by the American Cancer Society meet with the women to offer tips and advice about looking their best while being treated for cancer. The programs, which have been sponsored by the American Cancer Society since 1989, are free; the beauty products, which include makeup kits for participants to take home with them, are donated by the Personal Care Products Council.

As of 2016, there were 15,400 LGFB workshops available in 2,500 locations across the United States; some were just for teens or Spanish-speaking women. People can contact the LGFB program through their local American Cancer Society chapter or by calling 1-800-395- LOOK (5665). The program's website is .

How Do Patients Live with Breast Cancer?

Treatment for breast cancer can be very taxing emotionally and physically. Women who undergo a mastectomy face emotional difficulties and may also experience serious postoperative swelling in their arms. Chemotherapy carries a set of side effects as well. If the cancer has spread, individuals face the challenges of recognizing, planning for, and coping with the prospect of dying. Even if the breast cancer is successfully treated, patients must learn to live with the fear that the cancer might someday return.

See also Cancer: Overview • Cervical Cancer • Fibrocystic Breast Disorder • Genetic Diseases: Overview • Male Breast Enlargement • Ovarian Cancer • Tumor • Uterine Cancer


Books and Articles

American Cancer Society. Breast Cancer Clear & Simple: All Your Questions Answered. 2nd ed. Atlanta, GA: American Cancer Society, 2015.

Buckley, Julie, and Ankit Desai. Breast Cancer: Start Here: Everything You Need to Know about Integrative Health for the Newly Diagnosed. Jacksonville, FL: Water Street Press/HUN Books, 2014.


American Cancer Society. “What's New in Breast Cancer Research and Treatment?” (accessed April 12, 2016).

National Cancer Institute. “What You Need to Know about Breast Cancer.” (accessed April 12, 2016).


American Cancer Society. 250 Williams St. NW, Atlanta, GA 303031034. Toll-free: 800-227-2345. Website: (accessed April 12, 2016).

Breast Cancer and the Environment Research Program. Website: (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: (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.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)