The term “cancer” refers to a type of disease rather than to a single problem.
 

Cancer begins at the cellular level. A cell develops abnormally, then divides and multiplies, creating more abnormal cells. These cells do not function like normal body cells and, when there are sufficient numbers, they may create a mass, called a tumor, or they may crowd out the development of normal cells, as in cancers of the blood or lymph system.

Cancer can also spread as cells break away from the original site and travel through the bloodstream or lymph system to other parts of the body. This process is called metastasis and accounts for much of the seriousness of the disease.

Breast cancer means that the abnormal cells began multiplying in the breast. If the cancer is confined to the breast, it does not affect the function of vital organs.It is most common for breast cancer cells to spread by the lymph system. Breast cancer detected after it has spread to other organs in the body becomes more difficult to treat. 

The American Cancer Society offers a comprehensive description of breast cancer and defines the different stages of breast cancer.  Find out more.
 

The Susan G. Komen Breast Cancer Foundation also provides a page of information that discusses the different stages of breast cancer and the relative size of tumors that may be associated with each stage of breast cancer. Find out more.

What Breast Cancer Isn't ...

Every mass detected in your breast is not malignant, and finding a lump in your breast does not automatically mean you have breast cancer.

Conditions of the breast, such as fibrocystic breast changes may make your breasts feel lumpy. Even the texture of a normal breast may feel uneven in texture and somewhat lumpy. Also, many women experience certain “normal” changes in breast texture at different times in their lives. Some examples are listed below.

• Increase in size and density of breasts in the pre-menstrual phase of the monthly cycle, typically with an increase in tenderness.

 
• Enlargement of breasts during pregnancy and nursing as the milk ducts and glands prepare for and sustain lactation.

 
• Post-menopausal changes, as milk-producing structures lose the effects of hormone stimulation. 

 
• Hormone replacement therapy may result in still other changes in the texture of the normal breast.