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Questions About Cancer? 1-800-4-CANCER
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Breast Cancer Treatment (PDQ®)

General Information About Breast Cancer

Breast cancer is a disease in which malignant (cancer) cells form in the tissues of the breast.

The breast is made up of lobes and ducts. Each breast has 15 to 20 sections called lobe. Each lobe has many smaller sections called lobules. Lobules end in dozens of tiny bulbs that can make milk. The lobes, lobules, and bulbs are linked by thin tubes called ducts.

Drawing of female breast anatomy showing  the lymph nodes, nipple, areola, chest wall, ribs, muscle, fatty tissue, lobe, ducts, and lobules.
Anatomy of the female breast. The nipple and areola are shown on the outside of the breast. The lymph nodes, lobes, lobules, ducts, and other parts of the inside of the breast are also shown.

Each breast also has blood vessels and lymph vessels. The lymph vessels carry an almost colorless fluid called lymph. Lymph vessels carry lymph between lymph nodes. Lymph nodes are small bean-shaped structures that are found throughout the body. They filter substances in lymph and help fight infection and disease. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the chest.

The most common type of breast cancer is ductal carcinoma, which begins in the cells of the ducts. Cancer that begins in the lobes or lobules is called lobular carcinoma and is more often found in both breasts than are other types of breast cancer. Inflammatory breast cancer is an uncommon type of breast cancer in which the breast is warm, red, and swollen.

See the following PDQ summaries for more information about breast cancer:

Having a family history of breast cancer and other factors increase the risk of breast cancer.

Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn't mean that you will not get cancer. Talk with your doctor if you think you may be at risk.

Older age is the main risk factor for most cancers. The chance of getting cancer increases as you get older. Other risk factors for breast cancer include:

NCI's Breast Cancer Risk Assessment Tool uses a woman's risk factors to estimate her risk for breast cancer during the next five years and up to age 90. This online tool is meant to be used by a health care provider. For more information on breast cancer risk, call 1-800-4-CANCER.

Breast cancer is sometimes caused by inherited gene mutations (changes).

The genes in cells carry the hereditary information that is received from a person’s parents. Hereditary breast cancer makes up about 5% to 10% of all breast cancer. Some mutated genes related to breast cancer are more common in certain ethnic groups.

Women who have certain gene mutations, such as a BRCA1 or BRCA2 mutation, have an increased risk of breast cancer. These women also have an increased risk of ovarian cancer, and may have an increased risk of other cancers. Men who have a mutated gene related to breast cancer also have an increased risk of breast cancer. For more information, see the PDQ summary on Male Breast Cancer Treatment.

There are tests that can detect (find) mutated genes. These genetic tests are sometimes done for members of families with a high risk of cancer. See the PDQ summary on Genetics of Breast and Gynecologic Cancers for more information.

Decreasing the length of time a woman's breast tissue is exposed to estrogen decreases the risk of breast cancer.

Anything that decreases your chance of getting a disease is called a protective factor.

Protective factors for breast cancer include the following:

Signs of breast cancer include a lump or change in the breast.

These and other signs may be caused by breast cancer or by other conditions. Check with your doctor if you have any of the following:

  • A lump or thickening in or near the breast or in the underarm area.
  • A change in the size or shape of the breast.
  • A dimple or puckering in the skin of the breast.
  • A nipple turned inward into the breast.
  • Fluid, other than breast milk, from the nipple, especially if it's bloody.
  • Scaly, red, or swollen skin on the breast, nipple, or areola (the dark area of skin that is around the nipple).
  • Dimples in the breast that look like the skin of an orange, called peau d’orange.

Tests that examine the breasts are used to detect (find) and diagnose breast cancer.

Check with your doctor if you notice any changes in your breasts. The following tests and procedures may be used:

  • Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
  • Clinical breast exam (CBE): An exam of the breast by a doctor or other health professional. The doctor will carefully feel the breasts and under the arms for lumps or anything else that seems unusual.
  • Mammogram: An x-ray of the breast.
    Mammography; the left breast is pressed between two plates.  An X-ray machine is used to take pictures of the breast. An inset shows the x-ray film image with an arrow pointed at abnormal tissue.
    Mammography. The breast is pressed between two plates. X-rays are used to take pictures of breast tissue.
  • Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram. The picture can be printed to be looked at later.
  • MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of both breasts. This procedure is also called nuclear magnetic resonance imaging (NMRI).
  • Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.
  • Biopsy : The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. If a lump in the breast is found, the doctor may need to remove a small piece of the lump.

    There are four types of biopsy used to check for breast cancer:

If cancer is found, tests are done to study the cancer cells.

Decisions about the best treatment are based on the results of these tests. The tests give information about:

  • how quickly the cancer may grow.
  • how likely it is that the cancer will spread through the body.
  • how well certain treatments might work.
  • how likely the cancer is to recur (come back).

Tests include the following:

  • Estrogen and progesterone receptor test : A test to measure the amount of estrogen and progesterone (hormones) receptors in cancer tissue. If there are more estrogen and progesterone receptors than normal, the cancer is called estrogen and/or progesterone receptor positive. This type of breast cancer may grow more quickly. The test results show whether treatment to block estrogen and progesterone may stop the cancer from growing.
  • Human epidermal growth factor type 2 receptor (HER2/neu) test: A laboratory test to measure how many HER2/neu genes there are and how much HER2/neu protein is made in a sample of tissue. If there are more HER2/neu genes or higher levels of HER2/neu protein than normal, the cancer is called HER2/neu positive. This type of breast cancer may grow more quickly and is more likely to spread to other parts of the body. The cancer may be treated with drugs that target the HER2/neu protein, such as trastuzumab and pertuzumab.
  • Multigene tests: Tests in which samples of tissue are studied to look at the activity of many genes at the same time. These tests may help predict whether cancer will spread to other parts of the body or recur (come back).

Based on these tests, breast cancer is described as:

  • Hormone-receptor positive (estrogen and/or progesterone receptor positive) or hormone-receptor negative (estrogen and/or progesterone receptor negative).
  • HER2/neu positive or HER2/neu negative.
  • Triple negative (estrogen receptor, progesterone receptor, and HER2/neu negative).

This information helps the doctor decide which treatments will work best for your cancer.

Certain factors affect prognosis (chance of recovery) and treatment options.

The prognosis (chance of recovery) and treatment options depend on the following:

  • The stage of the cancer (the size of the tumor and whether it is in the breast only or has spread to lymph nodes or other places in the body).
  • The type of breast cancer.
  • Estrogen receptor and progesterone receptor levels in the tumor tissue.
  • Human epidermal growth factor type 2 receptor (HER2/neu) levels in the tumor tissue.
  • Whether the tumor tissue is triple-negative (cells that do not have estrogen receptors, progesterone receptors, or high levels of HER2/neu).
  • How fast the tumor is growing.
  • How likely the tumor is to recur (come back).
  • A woman’s age, general health, and menopausal status (whether a woman is still having menstrual periods).
  • Whether the cancer has just been diagnosed or has recurred (come back).
  • Updated: April 3, 2015