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; it is estimated that over 182,000 women were diagnosed with breast cancer in the US in 2008. Although the majority of breast cancer cases occur in women, men can develop it as well; approximately 2,000 men developed breast cancer in the US in 2008.
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.
Breast Anatomy and the Development of Breast Cancer
The breast consists of lobes, lobules, and bulbs that are connected by ducts. The breast also contains blood and lymph vessels. These lymph vessels lead to structures that are 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.
When breast cancer spreads outside the breast, cancer cells are most often found under the arm in the lymph nodes. In many cases, if the cancer has reached the lymph nodes, cancer cells may have also spread to other parts of the body via the lymphatic system or through the bloodstream.
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 is divided mainly into the pre-invasive or “in-situ” form, or the invasive or infiltrating form. The pre-invasive form is restricted to the breast itself and has not yet invaded any of the lymphatics or blood vessels that surround the breast tissue. Therefore, it does not spread to lymph nodes or other organs in the body. Treatments are generally local only and a cure is a reality for almost all patients.
- Ductal carcinoma in situ (DCIS)—This is the most common pre-invasive breast cancer. More 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). If left untreated, DCIS will progress to invasive 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 accidental, 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 invasive lobular carcinoma) over the next 20 years.
LCIS does not warrant treatment by surgery or radiation therapy. Close follow-up is most commonly indicated, and LCIS is not easily seen on mammogram. Recent data suggest that this condition may be a precursor to invasive lobular cancer. There may be some forms of LCIS that require more aggressive local therapy and closer follow-up.
- 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 —Paget's disease is cancer of the areola and nipple. It is very rare (about 1% of all breast cancers). In general, women who develop this type of cancer have a history of nipple crusting, scaling, itching, or inflammation.