Breast cancer is a disease in which cancer cells grow in the breast. Normally, the cells of the breast divide in a regulated manner. If cells keep dividing when new cells are not needed, a mass of tissue forms. This mass is called a tumor. A tumor can be benign or malignant.
A benign tumor is not cancer and will not spread to other parts of the body. A malignant tumor is cancer. Cancer cells divide and damage tissue around them. They can enter the bloodstream and spread to other parts of the body. This can be life-threatening.
Breast cancer is the most common form of cancer found in women, but lung cancer claims more lives. It was estimated that over 232,300 women would be diagnosed with breast cancer in the United States in 2013. Although the majority of breast cancer cases occur in women, it occurs in men as well. It was estimated that over 2,200 men would develop breast cancer in the US in 2013.
Caucasian, Hawaiian, and African American women have the highest rates of breast cancer in the US. The lowest rates occur among Korean, Native American, and Vietnamese women. The risk of breast cancer increases with age.
Normal Anatomy and the Development of Breast Cancer
The normal breast consists of glandular tissue called lobes. These lobes are sectioned off into lobules, which produce milk. Milk is carried from the lobules to the nipple by small ducts. All this tissue is surrounded by fatty and connective tissue, as well as blood and lymph vessels.
The lymph vessels lead to structures called lymph nodes. Clusters of lymph nodes are found under the arm, above the collarbone, in the chest, and in other parts of the body. Together, the lymph vessels and lymph nodes make up the lymphatic system, which circulates a fluid called lymph throughout the body. Lymph contains cells that help fight infection and disease. Although the lymphatic system is used to defend the body, it can also serve as a mechanism to spread cancer cells. Cancer can spread to other lymph nodes or to other parts of the body via the bloodstream.
Breast cancer can start anywhere in the breast tissue, but the most common places are in the ducts and lobules. If they remain undetected, cancer cells may form a tumor, or invade nearby tissue, such as the chest wall or lymph glands. When cancer is metastatic, it spreads to other parts of body replacing healthy tissue with cancerous tissue. The most common sites for metastatic breast cancer are the bones, lung, brain, and liver.
Types of Breast Cancer
Breast cancer can develop in different ways and may affect different parts of the breast. The location of cancer will affect the progression of cancer and the treatment.
Most breast cancers are carcinomas—malignant tumors that grow out of the surface or lining of the glandular tissue of the breast. Other very rare types of breast cancer are formed in the surrounding and supporting tissues, and your doctor may call these sarcomas, acinar tumors, or lymphomas.
Breast cancer can be classified by its invasiveness. In situ cancers are localized. This means the cancer is contained to the affected tissue only, and has not spread. Treatment for in situ cancers are generally local and a cure can be attained in most cases.
Infiltrating cancers, however, have begun to spread beyond the primary site. Depending on how long the cancer has been growing, invasion can occur in adjacent tissue or distant sites in the body.
- Ductal carcinoma in situ (DCIS)—Is commonly seen now because this form is generally seen on a mammogram and is identified by unusual calcium deposits or puckering of the breast tissue (called stellate appearance). This type of cancer has a high cure rate. However, if left untreated, DCIS will progress to infiltrating breast cancer.
- Lobular carcinoma in situ (LCIS)—Unlike DCIS, LCIS is not really cancer at all. Most doctors consider the finding of LCIS to be incidental, and it is thought to be a marker for breast cancer risk. That is, women with LCIS seem to have a 7-10 times increased risk of developing some form of breast cancer (usually infiltrating lobular carcinoma) over the next 20 years.
LCIS does not warrant treatment by surgery or radiation therapy. Your doctor will monitor your LCIS with regular check-ups and tests to see if there is any further development.
- Ductal carcinoma—This is the most common form of breast cancer and accounts for 70% of breast cancer cases. This cancer develops in the milk ducts.
- Lobular carcinoma—This originates in the milk-producing lobules of the breast. It can spread to the fatty tissue and other parts of the body.
- Medullary, mucinous, and tubular carcinomas —These are three relatively slower-growing types of breast cancer.
- Inflammatory carcinoma—This is the fastest growing and most difficult type of breast cancer to treat. This cancer invades the lymphatic vessels of the skin and can be very extensive. It is very likely to spread to the local lymph nodes.
Paget's disease is cancer of the areola and nipple. It is very rare, occurring in less than 1% of all breast cancers. Although Paget's does not arise from glandular tissue in the breast, it can be associated with both in situ and infiltrating breast cancers. Generally, women who develop this type of cancer have a history of nipple crusting, scaling, itching, or inflammation.
- Reviewer: Mohei Abouzied, MD, FACP
- Review Date: 12/2014 -
- Update Date: 12/20/2014 -