Cancer InDepth: Breast Cancer
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Breast cancer is a disease in which cancer cells originate and grow in the breast. Some tumors of the breast can be benign. Benign tumors are not considered breast cancer. Breast cancer involves cells that have the potential to invade and ultimately spread outside of the breast.
Breast cancer is the most common form of cancer found in women—it is estimated that over 180,000 women are diagnosed with invasive forms of breast cancer every year and 25,000 may be diagnosed with in situ or non-invasive forms of breast cancer. Although the majority of breast cancer cases occur in women, men can develop it as well; approximately 1,000 men develop breast cancer in the United States each year.
In the United States, Caucasian, Hawaiian, and African-American women have the highest rates of breast cancer. The lowest rates occur among Korean, Native American, and Vietnamese women.
The breast consists of lobules that produce milk and are connected to ducts that lead to the nipple. 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 nodes help fight infection and disease.
When breast cancer spreads outside the breast, cancer cells are 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. Cancer spread to the lymph nodes is a marker of risk of spread elsewhere, but in approximately 30% of patients who do not have cancer in the lymph nodes, breast cancer cells may have spread to other parts of the body.
Types of Breast Cancer
Most malignant tumors in the breast are known as carcinomas—malignant tumors that grow out of the surface or lining of the glandular tissues of the breast. Other very rare types of breast cancer are formed in the surrounding and supporting tissues. These may include sarcomas, acinar tumors, or lymphomas.
Breast cancer is divided mainly into the non-invasive (in situ) form and the invasive (infiltrating) form. The non-invasive form is restricted to the duct or lobule and has not yet invaded any of the tissue of the breast itself and certainly not the lymphatics or blood vessels that surround the ducts. Therefore, it almost never spreads to lymph nodes or other organs in the body. Treatments are generally local and cure over 99% of patients.
Non-invasive Forms of Breast Cancer
Ductal carcinoma in situ (DCIS) - the most common non-invasive breast cancer. This form is generally seen on a mammogram, and is identified by unusual calcium deposits. 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 physicians consider the finding of LCIS 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 over the next 20 years in either breast. LCIS does not warrant treatment with surgery or radiation therapy. Close follow up is most commonly indicated, however risk reduction strategies are often discussed including chemoprevention and in rare cases, bilateral mastectomy. LCIS is not easily seen on mammogram.
Invasive Forms of Breast Cancer
Ductal carcinoma – this is the most common form of breast cancer and accounts for 70% of breast cancer cases. This form develops in the milk ducts. Invasive ductal cancer can include subtypes known as medullary, mucinous, and tubular carcinomas.
Lobular carcinoma – originates in the milk-producing lobules of the breast.
Inflammatory carcinoma – the fastest growing and most difficult type of breast cancer to treat. This cancer invades the lymphatic vessels of the skin and can arise very quickly. It is very likely to spread to the local lymph nodes.
Paget’s Disease – Paget’s disease is an unusual condition where cells may affect the areola or the nipple. In general, women who develop this type of cancer have had a history of nipple crusting, scaling, itching, or inflammation. Paget’s disease rarely is isolated and most often signifies an underlying cancer affecting the breast.
This Report Covers the Following:
National Cancer Institute
The National Women’s Health Information Center
Harris JR, Lippman ME, Morrow M, Osborne CK. Diseases of the Breast . Philadelphia: Lippincott Williams and Wilkins; 1999.
Last reviewed February 2003 by
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