Breast cancer is a disease in which malignant (cancerous) cells form in the breast tissue.
The breast is made up of glandular lobes and ducts. Each breast has 15 to 20 lobes. Each lobe has many lobules. The lobules end in dozens of vesicles that make milk. The lobes, lobules, and follicles are connected by thin tubes called ducts.
Anatomy of the female breast. The nipple and areola are shown on the outside of the breast. The others are the lymph nodes, lobes, lobules, ducts, and other parts of the interior of the breast.
Each breast also has blood vessels and lymphatic vessels. The lymphatic vessels carry an almost colorless, watery fluid called lymph. Lymphatic vessels carry lymph between lymph nodes. Lymph nodes are small, bean-shaped structures that are spread throughout the body. They filter lymph and store white blood cells that help fight infection and disease. Multiple sets of lymph nodes are found in the armpits (underarms), above the collarbone, and near the breast in the chest.
The most common type of breast cancer is ductal carcinoma, which begins in the ductal cells. Those that begin in the lobes or lobules are called lobular carcinomas and are more common in both breasts than other types of breast cancer. Inflammatory breast cancer is a rare type of breast cancer that presents as heat, redness, and swelling of the breast.
For more information about breast cancer, see the following PDQ summaries:
Breast cancer prevention
Breast Cancer Screening
Treatment of Breast Cancer in Pregnancy
Male breast cancer treatment
Treatment of breast cancer in children
A family history of breast cancer and other factors can increase the risk of developing breast cancer.
Any factor that increases the chance of developing the disease is called a risk factor. Having a risk factor does not mean that you will definitely get cancer; not having a risk factor does not mean that you will not get cancer. If you think you are at risk, talk to your doctor.
Risk factors for breast cancer include:
Personal history of previous invasive breast cancer, intraductal breast carcinoma in situ, or lobular breast carcinoma in situ.
History of benign (non-cancerous) breast disease.
Have a family history of breast cancer in a first-degree relative (mother, daughter, or sister).
Hereditary variants of the BRCA1 or BRCA2 genes or other genes that increase the risk of breast cancer.
Dense breast tissue in mammograms.
Breast tissue is exposed to estrogen produced by the body. This may be due to the following.
Little age at menarche
Older age at menarche or never having given birth
Menopause at an older age
taking hormones, such as taking both progesterone and estrogen in response to certain menopausal symptoms
Receiving radiation therapy to the breast/chest
Drinking alcohol
Obesity.
Age is a major risk factor for most cancers. As you get older, your chances of getting cancer increase.
The National Cancer Institute’s (NCI) Breast Cancer Risk Assessment Tool uses a woman’s risk factors to assess her risk of developing breast cancer over the next 5 years to age 90. The online tool is applied by medical professionals. To see more information on breast cancer risk, call 1-800-4-CANCER.
Breast cancer is sometimes the result of an inherited genetic mutation (variant).
The genes in the cell carry genetic information received from the parents. Hereditary breast cancer accounts for about 5% to 10% of all breast cancers. Certain mutated genes that are associated with breast cancer are more common in certain specific ethnic groups.
Women with certain gene mutations, such as the BRACA1 or BRACA2 mutations, are at higher risk for breast cancer. These women also have a higher risk of developing ovarian cancer and may have a higher risk of developing other cancers. Men with breast cancer-related mutations also have a higher risk of developing breast cancer. For more information, see the PDQ summary on the treatment of male breast cancer.
Some tests can be used to find mutated genes. These genetic tests are sometimes used for family members who have a higher risk of breast cancer. For more information, see the PDQ summary on genetics of breast and gynecologic cancers.
The use of certain drugs and other methods can reduce the risk of breast cancer.
Any factor that reduces the risk of developing a certain disease is called a protective factor.
Breast cancer-related protective factors include the following:
The following may be used.
Estrogen-only therapy after hysterectomy
Selective estrogen receptor modulators (SERMs)
Aromatase inhibitors
Mammary tissue is less exposed to estrogen produced by the body. This may be due to.
early pregnancy
breastfeeding
Adequate exercise.
Undergoing any of the following surgeries.
mastectomy to reduce the risk of cancer
Oophorectomy to reduce the risk of cancer
Ovarian removal
Signs of breast cancer include a lump or change in the breast.
These and other signs may be caused by breast cancer or other causes. Consult your doctor if you have any of the following:
A swelling or thickening in or around the breast or near the armpit
A change in the size or shape of the breast.
Depression or wrinkling of the skin of the breast
Depression of the nipple inward.
Non-breast milk fluid flowing from the nipple, especially if it is bloody.
Scaly, red or swollen skin on the breast, nipple or areola (the dark area around the nipple).
A dimple on the breast that looks like an orange peel is called an “orange peel lesion.
Breast-related tests can be used to detect and diagnose breast cancer.
Consult your doctor if you notice any changes in your breasts. The following tests and methods are available:
Examination and history: An examination of the body to check for general signs of health, including examination for signs of disease, such as lumps or anything that looks abnormal. The patient’s health habits, past history, and treatment history are also referred to.
A clinical breast exam is an examination performed by a doctor or other health professional. The doctor will carefully palpate the breast and underarm for lumps or anything else that looks abnormal.
Mammogram: For an X-ray of the breast. 
Mammography The breast is pressed between two plates. X-rays are used to take images of the breast tissue.
Ultrasound: An exam in which high-energy sound waves (ultrasound) are reflected off of internal tissues or organs and produce echoes. These echoes form an image of the body’s tissues called a sonogram. The images can be printed and used for later viewing.
Magnetic resonance imaging (MRI): A method that uses magnets, radio waves, and a computer to image internal areas of the body in a series of details, also called nuclear magnetic resonance imaging (NMRI).
Blood chemistry verification: A method that checks the amount of certain substances (such as bilirubin or lactate dehydrogenase (LDH)) released by organs and tissues in a blood sample. Abnormal levels of a substance (higher or lower than normal) may be a sign of disease.
Biopsy: A portion of cells or tissue is removed and looked at by a pathologist under a microscope to check for signs of cancer. If a lump is found in the breast, a biopsy may be performed.
There are four types of biopsies that can be used to check for breast cancer:
Excisional biopsy: Removal of a whole piece of tissue.
Excisional biopsy: Removal of a portion of the lump or tissue sample.
Hollow needle biopsy: Use a thick needle to remove tissue.
Fine needle aspiration biopsy: Use a fine needle to remove tissue or body fluid.
If cancer is detected, more tests are needed to study the cancer cells.
Make a judgment about what treatment options are best based on the results of these tests. These tests help to know:
How fast the cancer is likely to spread.
How likely it is that the cancer will spread throughout the body.
How well certain therapies work
How likely the cancer is to come back.
These tests include:
Estrogen and progesterone receptor test: a test that measures the amount of estrogen and progesterone (hormone) receptors in cancer tissue. If estrogen and progesterone receptors are higher than normal, the cancer is said to be estrogen and/or progesterone receptor positive. This type of breast cancer may grow more rapidly. The test results may indicate whether treatment to block estrogen and progesterone may stop the development of the cancer.
Human epidermal growth factor type 2 receptor (HER2 / neu) test: A laboratory test that measures how many HER2 / neu genes are present in a tissue sample and how much HER2 / neu protein is produced. If there is a greater than normal amount of the HER2 / neu gene, the cancer is said to be HER2 / neu positive. This type of breast cancer may grow more quickly and is more likely to spread to other parts of the body. Drugs that target the HER2 / neu protein (such as trastuzumab and patuximab) may be used to treat this cancer.
Multigene testing: Simultaneous testing for patterns of activity of multiple genes in tissue samples. This testing helps predict whether the cancer will spread to other parts of the body and whether it will recur.
There are many types of polygenic tests. The following polygenic tests have been studied in clinical trials:
Cancer DX: This test helps predict whether estrogen receptor-positive and lymph node-negative early-stage breast cancer will spread to other parts of the body. If the risk of cancer spreading is high, chemotherapy may be given to reduce the risk.
MammaPrint: A laboratory test that looks at the activity of 70 different genes in breast cancer tissue from women with early invasive breast cancer that has not spread to lymph nodes or has spread to 3 or fewer lymph nodes. The activity levels of these genes help predict whether breast cancer will spread to other parts of the body or whether it will recur. If the test shows a high risk of the cancer spreading or coming back, chemotherapy may be given to reduce the risk.
Based on these tests, breast cancer can be described as one of the following types:
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 will help your doctor decide which therapies will be most effective in treating your cancer.
Some factors also affect prognosis (chance of recovery) and choice of treatment options.
Prognosis and treatment options depend on the following factors:
Stage of the cancer (the size of the tumor and whether it is only in the breast or has spread to the lymph nodes or other parts of the body).
Type of breast cancer.
The level of estrogen receptors and progesterone receptors in the tumor tissue.
levels of human epidermal growth factor type 2 receptor (HER2 / neu) in tumor tissue
Whether the tumor tissue is triple negative (cells without estrogen receptors, progesterone receptors, or high levels of HER2/neu)
How fast the tumor is growing.
How likely the tumor is to recur.
The woman’s age, overall health, and menopausal status (whether she is menopausal).
Whether the cancer has just been diagnosed or is a recurrence.