Definition and Function of Lymph Nodes

Lymph nodes, also known as lymph glands, are oval-shaped masses of tissue in the body that serve an important role in protecting the body from infection and cancer. By answering these basic questions about lymph nodes, you will gain an understanding of the role they play in your or your loved one's cancer or infection.

Everyone has an extensive lymphatic system in their body, which consists of lymph nodes and lymph vessels. The lymph vessels carry a clear fluid called lymph that is collected from tissues throughout the body. Lymph contains cell wastes like cancer cells, bacteria, and viruses. This fluid then drains into lymph nodes where it's filtered by infection-fighting cells within the lymph nodes. These infection-fighting cells, also called white blood cells, destroy these foreign or "bad"  cancer and infection-related cells. 

A sign that immune cells within a lymph node are fighting an infection or cancer is when they enlarge or become swollen. This is called lymphadenopathy, or adenopathy for short. 

Lymph nodes are scattered throughout the body and located in groups, like in the armpit, groin, neck, pelvis, and abdomen. In some areas like the neck, the lymph nodes are located superficially and may be palpated — they feel like a pea or small bean. In other areas, like the abdomen or the chest, lymph nodes are located deeper and cannot be felt.

Enlarged or swollen lymph nodes can indicate infection, cancer, or another disease that affects the immune system. Most typically, swollen lymph nodes are related to a minor infection that the immune system is fighting. For example, one or more lymph nodes in the neck may become swollen and tender with an ear infection, sore throat, or tooth abscess. Once the infection has cleared, swollen lymph nodes shrink back to their normal size.

Nodes that are immobile, hard, non-tender, and persistently enlarged are suspicious for cancer and should be evaluated by a physician. If cancer cells are present in a lymph node, they either spread there from the primary tumor — like a breast tumor that spreads to lymph nodes in the armpit — or they originate in the lymph node, and this is called lymphoma. If a person is diagnosed with a solid tumor, whether or not certain lymph nodes are enlarged is an important part of cancer staging, which affects how that cancer is treated. 

Tonsils are considered lymphatic organs and act as lymph nodes, although they are much larger. The spleen — an organ located on the left side of your abdomen — is also a lymphoid organ, although instead of filtering lymph fluid, it filters blood. 

If your doctor is concerned that a lymph node is affected by cancer or infection, he will take a biopsy of the lymph node or remove the entire lymph node. The contents of the lymph node can then be examined under a microscope by a pathologist to see if cancer or infection-related cells are present.