About Breast Cancer
What is Cancer?

Cancer is a group of more than 100 different diseases. Cancer occurs when, for unknown reasons, cells become abnormal and divide without control or order. All parts of the body are made up of cells that normally divide to produce more cells only when the body needs them. When cancer occurs, cells keep dividing even when new cells are not needed.

The change from normal to cancerous cells requires several separate, different gene alterations. Eventually, altered genes and uncontrolled growth may produce a tumor that can be benign (not cancer) or malignant (cancer). Malignant tumors can invade, damage, and destroy nearby tissues and spread to other parts of the body. A benign tumor won't spread to other parts of the body, but local tissue may be damaged and the growth may need to be removed.

To learn more about breast lumps and other breast changes, read NCI's booklet Understanding Breast Changes: A Health Guide for All Women, available from the Cancer Information Service. It includes information about many breast changes that are not cancer and explains the procedures used to discover the presence of breast cancer.

Types of Breast Cancer

There are several types of breast cancer. The most common is ductal carcinoma, which begins in the lining of the milk ducts of the breast. Another type, lobular carcinoma, begins in the lobules where breast milk is produced. If a malignant tumor invades nearby tissue, it is known as infiltrating or invasive cancer.

How Cancer Spreads

A malignant tumor can invade surrounding tissue and destroy it. Cancer cells can also break away from a malignant tumor and enter the bloodstream or the lymphatic system. This is how cancer spreads within the body. When breast cancer spreads outside the breast, cancer cells often are found in the lymph nodes under the arm. Cancer cells may spread beyond the breast such as to other lymph nodes, the bones, liver, or lungs. (Although it is not common, some patients whose underarm lymph nodes are clear of breast cancer may still have cancer cells which have spread to other parts of the body.)

Cancer that spreads to other parts of the body is the same disease and has the same name as the original cancer. When breast cancer spreads, it is called metastatic breast cancer even though it is found in another part of the body. For example, breast cancer that has spread to the bones is called metastatic breast cancer, not bone cancer.

What Causes Breast Cancer?

Medical researchers are learning about what happens inside cells that may cause cancer. They have identified changes in certain genes within breast cells that can be linked to a higher risk for breast cancer. Breast cells contain a variety of genes that normally work cooperatively with a woman's natural hormones, diet, and environment to keep her breasts healthy. Certain genes routinely keep breast cells from dividing and growing out of control and forming tumors. When these genes become altered, changes occur and a cell no longer can grow correctly.

Genetic changes may be inherited from a parent or may accumulate throughout a person's lifetime. Breast cancer usually begins in a single cell that changes from normal to malignant over a period of time. Presently, no one can predict exactly when cancer will occur or how it will progress. When breast cancer is diagnosed - even if detected at the earliest stage - it is not yet possible to predict which cancer cells will be treated successfully and which will continue to grow and spread quickly to other parts of the body.

What is known:

* You should not feel guilty. You haven't done anything wrong in your life that caused breast cancer.
* You cannot "catch" breast cancer from other women who have the disease. It is not contagious.
* Breast cancer is not caused by stress or by an injury to the breast.
* Most women who develop breast cancer do not have any known risk factors or a history of the disease in their families.

Who Gets Breast Cancer?

Every woman has some chance of developing breast cancer during her lifetime. As women get older, their chances increase. Breast cancer is the most frequently diagnosed cancer in women in the United States today, other than skin cancer. Even though breast cancer is more common in older women, it also occurs in younger women and even in a small number of men.

Gene Testing

Medical researchers are now able to look within cells, and are making new discoveries that explain how genes are related to cancer and other diseases. They have identified specific genes linked to breast cancer and other cancers that run in families. Tests are becoming available for women and family members who choose to find out if they have inherited the genetic changes that increase their risk for cancer. There is still much uncertainty involved with gene testing. If you or your family members are considering testing, your doctor or a genetics counselor can give you guidance and help you make an informed decision. It's important to consider carefully the benefits, risks, limitations, and the far-reaching consequences of gene testing.