Breast Cancer Overview

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.

• Types 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.

All cancers are believed to begin with a mutation in a single cell. However, a cell doesn't become cancerous overnight. Several mutations in a row are necessary to create all the characteristic features of cancer. Ordinarily, cells have a self-destruct mechanism that causes them to die when their DNA is damaged. However, in developing cancer cells, something interferes with the self-destruct sequence. It may be that the cancer-causing mutations themselves turn off the countdown.

The DNA alterations that create a cancer cell give it a certain independence from the ordinary rules of cell behavior. Normal cells are highly influenced by nearby cells, with the result that they "get along" well with their neighbors. For example, the growth of a healthy cell is ruled by special growth factors given off by surrounding tissues. However, cancer cells either grow without such growth factors or simply make their own. Many types of cancer cells can also trigger the growth of new blood vessels to feed them.

The rate of cancerous mutations is increased by exposure to carcinogenic substances. Cigarette smoke is a powerful carcinogen. Many carcinogens exist in the diet as well, even in fruits and vegetables. This is why so many lifestyle treatments are said to prevent and even help treat cancer. Read more at Treatments for Breast Cancer.

Cancer is the second major cause of death (next to heart disease) in the United States. It claims the lives of more than half a million Americans each year out of the nearly 1.4 million who get the disease. The probability of getting cancer increases with age. Two-thirds of all cases are in people older than 65.¹

Breast cancer. National Cancer Institute website. Available at: http://www.cancer.gov . Accessed January 31, 2006.

Breast cancer. Womens' Health.gov website. Available at: http://www.4woman.gov . Accessed January 27, 2006.

1. Longo D. Approach to the patient with cancer. In: Fauci AS, Wilson JD, Martin JB, et al, eds. Harrison's Principles of Internal Medicine. 14th ed. New York, NY: McGraw-Hill; 1998.