What is cancer?
The body is made up of various kinds of cells, which normally divide in an orderly way to produce more cells only when they are needed. Cancer is a group of diseases -- more than 100 types -- that occur when cells become abnormal and divide without control or order.

What is a tumor?
When cells divide when new cells are not needed, too much tissue is formed. This mass of extra tissue, called a tumor, can be benign or malignant.

• benign tumors:

• are not cancerous

• can usually be removed

• do not come back in most cases

• do not spread to other parts of the body and the cells do not invade other tissues

• malignant tumors:

• are cancerous

• can invade and damage nearby tissues and organs

• metastasize -- cancer cells can break away from a malignant tumor and enter the bloodstream or lymphatic system to form secondary tumors in other parts of the body

• The most common type begins in the lining of the ducts and is called ductal carcinoma.

• Another common type, called lobular carcinoma, occurs in the lobules.

When breast cancer metastasizes, or spreads outside the breast, cancer cells are often found in the lymph nodes under the arm. If the cancer has reached these nodes, it may mean that cancer cells have spread to other parts of the body.

Cancer that spreads is the same disease and has the same name as the original, or primary cancer. When breast cancer spreads, it is called metastatic breast cancer, even though the secondary tumor is in another organ. This may also be called "distant" disease.

Types of breast cancer, in alphabetical order, are:

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