In the United States, breast cancer is the most common cancer in women (excluding skin cancer). Men can also develop breast cancer, but male breast cancer is rare, accounting for less than 1% of all breast cancers.
About the breast
The breast is mostly made up of fatty tissue. Within this tissue is a network of lobes, which are made up of tiny, tube-like structures called lobules that contain milk glands. Tiny ducts connect the glands, lobules, and lobes, carrying the milk from the lobes to the nipple, located in the middle of the areola (darker area that surrounds the nipple). Blood and lymph vessels also run throughout the breast; blood nourishes the cells, and the lymph system drains bodily waste products. The lymph vessels connect to lymph nodes, the tiny, bean-shaped organs that help fight infection.
About breast cancer
Cancer begins when normal cells in the breast change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
Breast cancer spreads when breast cancer cells move to other parts of the body through the blood vessels and/or lymph vessels. This is called metastasis. Breast cancer most commonly spreads to the regional lymph nodes. The lymph nodes can be axillary (located under the arm), cervical (located in the neck), or supraclavicular (located just above the collarbone). When it spreads further through the body, it most commonly spreads to the bones, lungs, and liver. Less commonly, breast cancer may spread to the brain. The cancer can also recur (come back after treatment) locally in the skin, in the same breast (if it was not removed as part of treatment), other tissues of the chest, or elsewhere in the body.
Types of breast cancer
Most breast cancers start in the ducts or lobes. Almost 75% of all breast cancers begin in the cells lining the milk ducts and are called ductal carcinomas. Cancer that begins in the lobules is called lobular carcinoma. If the disease has spread outside of the duct and into the surrounding tissue, it is called invasive or infiltrating ductal carcinoma. If the disease has spread outside of the lobule, it is called invasive or infiltrating lobular carcinoma. Disease that has not spread is called in situ, meaning “in place.” How in situ disease grows and spreads, as well as how it is treated, depends on whether it is ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS).
Most in situ breast cancers are DCIS. Currently, oncologists recommend surgery to remove DCIS to help prevent the cancer from becoming an invasive breast cancer and spreading to other parts of the breast or the body. Radiation therapy and hormonal therapy may also be recommended for DCIS (see Treatment for more information).
LCIS is not considered cancer and is usually monitored by the doctor. LCIS is a risk factor for breast cancer (see the Risk Factors section for more information).
Other, less common cancers of the breast include medullary, mucinous, tubular, metaplastic, and papillary breast cancer. Inflammatory breast cancer is a faster-growing type of cancer that accounts for about 1% to 5% of all breast cancers. It may be misdiagnosed as a breast infection because there is often swelling of the breast and redness of the breast skin. Paget’s disease is a type of cancer that begins in the ducts of the nipple. The skin often appears scaly and may be itchy. Although it is usually in situ, it can also be an invasive cancer.
Find out more about basic cancer terms used in this section.
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Last Updated: January 26, 2012
