Lymph nodes are small, bean-shaped organs that help fight infection and are found throughout the body. They produce and filter a colourless fluid called lymph, which contains white blood cells known as lymphocytes (immune cells involved in defending against infections and such diseases as cancer).

Lymph vessels filter and carry lymph fluid from the breast to the lymph nodes. Clusters of lymph nodes near the breast are located in the armpit (known as axillary lymph nodes), above the collarbone, in the neck, and in the chest.