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 lobes, which have many smaller sections called lobules. Lobules end in dozens of tiny bulbs that can produce milk. The lobes, lobules, and bulbs are linked by thin tubes called ducts.
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 contains blood vessels and lymph vessels. The lymph vessels carry an almost colorless fluid called lymph. Lymph vessels lead to organs called 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.
See the following PDQ summaries for more information about breast cancer:
- Breast Cancer Prevention
- Breast Cancer Treatment
- Genetics of Breast and Ovarian Cancer
Breast cancer is the second leading cause of death from cancer in American women.
Women in the United States get breast cancer more than any other type of cancer except for skin cancer. Breast cancer is second only to lung cancer as a cause of cancer death in women.
Breast cancer occurs more often in white women than in black women. However, black women are more likely than white women to die from the disease.
Breast cancer occurs in men also, but the number of cases is small.
Health history can affect 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 for breast cancer. Risk factors for breast cancer include:
- Having certain gene mutations (changes), such as in the BRCA1 or BRCA2 genes.
- Menstruating at an early age.
- Older age at first birth or never having given birth.
- A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), or benign (noncancer) breast disease.
- A family history (first degree relative, such as a mother, daughter or sister) with breast cancer.
- Treatment with radiation therapy to the breast/chest.
- Breast tissue that is dense on a mammogram.
- Taking hormones such as estrogen and progestin for symptoms of menopause.
- Taking oral contraceptives ("the pill").
- Not getting enough exercise.
- Drinking alcoholic beverages.
- Being white.
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.