Lymph Nodes: Where They Are & Why They Matter in Breast Cancer

Lymph nodes play a key role in the lymphatic system. They are small organs that help fight infection and filter fluid called lymph that moves through vessels in the body. Lymph nodes trap bacteria, viruses, and other unwanted substances found in lymph and safely remove them from the body. 

Breast cancer cells that have escaped the original tumor often travel to nearby lymph nodes. The presence or absence of cancer in lymph nodes near the breasts is one of the most important signposts your doctor will use to determine the best cancer treatment for you.

If you’ve been diagnosed with breast cancer, your doctor may recommend you have surgery to remove anywhere from 1 to 10 or more lymph nodes so they can be checked for cancer. This may occur during a breast cancer surgery or during a separate surgery.

There are hundreds of lymph nodes located throughout the body. These nodes tend to be clustered under the arms and in the neck, abdomen, chest, and groin. Each lymph node filters fluid from the vessels that lead to it. 

Breast tissue drains into three main lymph node groups:

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  the nodes in your armpit (called axillary lymph nodes)

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  the nodes around your collarbone and neck (called the supraclavicular, infraclavicular, and cervical lymph nodes)

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  the nodes located on your chest (called parasternal/internal mammary lymph nodes)

Most lymph from the breast drains into the axillary nodes located near your armpit. These are the nodes that your healthcare team will check for cancer cells that may have traveled from a breast tumor.

Although many lymph nodes are located in the breast region, there are only a few sentinel lymph nodes — the nodes where lymph from the breast travels first. If breast cancer cells spread to the lymph nodes, they pass through the sentinel lymph nodes. Doctors check sentinel lymph nodes to better understand if breast cancer may have started to spread. 

To determine the location of sentinel lymph nodes, a surgeon injects a blue dye, radioactive liquid, or both into the breast tissue. The nodes that collect the greatest amount of radioactivity or dye are the sentinel nodes.

During a sentinel lymph node biopsy, a surgeon may only have to remove one lymph node, or they may have to remove a small cluster of two or three nodes. A pathologist checks these sentinel nodes for cancer. If cancer cells are found, additional lymph nodes may need to be removed. This procedure is called an axillary lymph node dissection.

The number of lymph nodes in the armpit area (axilla) is different for everyone, but can range from between 20 and 40 nodes. 

During an axillary lymph node dissection, surgeons remove a specific area of tissue from the axilla. A pathologist then identifies each lymph node in this tissue and checks for cancer. Typically, this will include  10 to 20 lymph nodes.