Breast Cancer: An Overview with Basic Terms

If found at an early stage, breast cancer can be easily treated.
If found at an early stage, breast cancer can be easily treated.

Breast cancer occurs when cells in the breast tissue start to grow out of control. All cells in the body go through a process of copying their genetic information and making new cells to replace old cells as they die. However, cancerous cells may copy the genetic information wrong, making more cancerous cells instead of normal healthy cells.

In the breasts, cancers can start in the cells that line the milk ducts (ductal cancers), in the milk-producing glands known as lobules (lobular cancers) or in the fatty and connective tissues of the breast, called stroma. Invasive breast cancer starting in the milk ducts is the most common form of breast cancer.


These out-of-control cells form a clump, called a tumor. That tumor may start to metastasize, or spread, forming new tumors in the breast tissue or other parts of the body. One of the first places that breast cancer spreads to is the area under the arms, where lymph nodes reside. From there, it is possible for cancerous cells to take advantage of the lymphatic system or blood stream and spread to other organs and bones.

Diagnosing Breast Cancer

An estimated 211,000 women will be diagnosed with breast cancer this year, and 40,000 will die from the disease. It is possible, but rare, for men to have breast cancer. About 1,700 men are diagnosed each year with breast cancer.

When someone is first tested for cancer, the doctor will want to take a biopsy of any suspicious lumps or tissues. This means that a small sample of cells will be removed and tested. Some tumors are benign, which means they are harmless. Others are malignant. Those are the ones that need to be removed or treated because they are likely to spread.

One thing the doctor will want to know is whether the cancer is invasive, which means it is likely to spread, or in situ, which means it is currently isolated to the tissue where it began. Most cancers are a combination.

The name of the cancer tells a lot about where it is located. For example, ductal carcinoma in situ — the most common kind of breast cancer — is cancer that is isolated to the tissue of the milk ducts.

The doctor will also find out about the stage of the cancer, which is a measure of how developed it is, including whether it has spread to other parts of the body. Stages range from 0 (early, small and not spread) to IV (very far progressed and spread).

All cancers can be thought of as out-of-control cells, but they also are all different. Breast cancers are not treated the same way that skin or brain cancers are treated, even though the basic concept is the same. Also, treatments will vary among women based on individual needs and the type of breast cancer.

However, while differing for different cancers and individuals, breast cancer treatment also uses standard approaches:

  • Surgery to remove cancerous tumors.
  • Chemotherapy using medications that either fight the cancer cells or help the body's immune system fight cancer cells.
  • Radiation treatment that essentially burns away cancer cells.

For more information about breast cancer, see the links on the next page.


Lots More Information

Related Articles

  • The American Cancer Society, "Detailed Guide: Breast Cancer"
  • National Cancer Institute, U.S. National Institutes of Health

Written by Madeline Roberts Vann, MPH

Reviewed by Susan L. Luedke, MD

St. Louis Cancer & Breast Institute

St. Louis University Medical Center

Last updated September 2008