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 make 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 has 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 a fluid called 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:
- Breast Cancer Prevention
- Breast Cancer Screening
- Breast Cancer Treatment and Pregnancy
- Male Breast Cancer Treatment
- Unusual Cancers of Childhood (for information about childhood breast cancer)
Health history can affect the risk of developing 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. Risk factors for breast cancer include the following:
- A family history (first-degree relative, such as mother, daughter, or sister) of breast cancer.
- Inherited changes in the BRCA1 and BRCA2genes or in other genes that increase the risk of breast cancer.
- Drinking alcoholic beverages.
- Breast tissue that is dense on a mammogram.
- Estrogen (made in the body)
- Menstruating at an early age.
- Older age at first birth or never having given birth.
- Taking hormones such as estrogen combined with progestin for symptoms of menopause.
- Taking oral contraceptives ("the pill").
- Not getting enough exercise.
- A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
- A personal history of benign (noncancer) breast disease.
- Being white.
- Treatment with radiation therapy to the breast/chest.