The lymphatic system is a network of tiny vessels that collect fluid and waste products from the body’s tissues.

This fluid is called lymph. Lymphatic vessels take the lymph to small glands called lymph nodes where substances that could be harmful to the body, such as bacteria or cancer cells, are trapped and removed. This helps to protect the body from infection. The lymph then passes back into the blood.

Lymph nodes are small, rounded glands that can range in size from about 1 mm to 25 mm.

There are lymph nodes all around the body, including the armpit, groin, stomach, chest and neck. The number of lymph nodes varies in different people. There are usually around 15–30 lymph nodes in the armpit.

Illustration of lymph nodes near the breast
Illustration of lymph nodes near the breast

Why are lymph nodes important in breast cancer?

The lymph nodes in the armpit (axilla) drain lymph fluid from nearby areas, including the breast.

The lymph nodes in the armpit are often the first place that cancer cells spread to outside the breast. About one in three women with breast cancer have cancer cells in the lymph nodes in their armpit when their breast cancer is diagnosed.

If there are cancer cells in the lymph nodes in the armpit, it may be possible to feel a lump in the armpit. However, many women are not aware of any changes. Cancer cells in the lymph nodes can usually only be seen under a microscope and cannot be felt or seen on X-rays or scans.

Lymph nodes can become enlarged for many reasons, including having a cold or an infection. If there is a lump in the armpit, this does not necessarily mean that cancer has spread to the armpit.