How does breast cancer spread?

If cancer spreads to other parts of the body, it’s called metastasis (muh-TASS-tuh-siss). Breast cancer can spread to other parts of the body in 3 ways:

1. Invading nearby healthy tissue, such as the chest wall.
2. Invading the lymphatic (lim-FAT-ihk) system. This system, which is part of the immune system, contains a network of lymph nodes (small, bean-shaped glands) and lymph vessels (thin tubes) that are found throughout the body. Lymph vessels carry a fluid called lymph to the lymph nodes, where it is filtered and checked for signs of infection and disease. Cancer cells can enter into lymph vessels in the breast and travel to the lymph nodes and other parts of the body. The first place breast cancer usually spreads is to the lymph nodes under the arms, called axillary (ak-suh-LAIR-ee) lymph nodes. That is why after breast cancer has been diagnosed, the underarm lymph nodes are often removed and examined to see if breast cancer has spread.
3. Invading blood vessels in the breast. Cancer cells can travel through the blood stream to other parts of the body, such as the lungs or bones.

When cancer cells spread, they can cause tumors to grow in other parts of the body. Breast cancer that forms tumors in other parts of the body, such as the lungs, is still breast cancer. The good news is that most breast cancers can be found and treated and do not come back in distant parts of the body.