How Lymph Nodes Determine Cancer Stage

You may have heard people talk about cancer stages and lymph nodes. But what does that really mean? When cancer spreads from one organ to other parts of the body, it typically gets there via the lymphatic system. The lymphatic system is made up of different organs, like the spleen, bone marrow, along with lymph nodes and lymph fluid. 

In this article, we explain the lymphatic system and how lymph nodes help determine cancer stage (how severe it is). 

What is the lymphatic system? 

The lymphatic system is like the body’s sewer system. Sewers in our cities drain extra stormwater from the streets. Then sewage plants clean the fluid so it can safely return to the environment.

The lymphatic system does the same thing in the body. In this case, the stormwater is lymphatic fluid, and the sewage plants are the lymph nodes. Lymph nodes are pea-sized balls of tissue that act as the body’s filters. They clean the lymphatic fluid before returning it to the rest of the bloodstream via a vein near the heart.  

What do lymph nodes do?

Lymph nodes are part of the immune system — the body’s army. The immune system protects you from foreign invaders, like infections and cancers. Lymph nodes contain immune cells that kill infections and cancer cells, filtering out what doesn’t belong.

There are hundreds of lymph nodes throughout the body. You may be able to feel some of them under the skin with your fingers in areas like the neck, armpits, or groin. Others are deeper in the body (like the abdomen). Lymph nodes are connected by lymphatic vessels, which are like blood vessels, but thinner and full of clear lymphatic fluid. 

What causes swollen lymph nodes?

Lymph nodes can swell when something activates the immune system, like an autoimmune condition or allergic reaction to medication. Lymph nodes also swell when they find something to filter out, like infection or cancer cells. They return to their normal size after the immune cells remove what doesn’t belong.   

There are many different causes of swollen lymph nodes (lymphadenopathy), and most of them aren’t cancer. For example, a throat infection can cause swelling of lymph nodes in the neck. Or a virus may cause swelling of many lymph nodes throughout the body. 

If you have swollen lymph nodes, your healthcare provider will ask questions about your symptoms and carefully examine you to find the cause. If swelling lasts more than a few weeks, they may recommend additional tests to help figure it out. 

What is the relationship between lymph nodes and cancer?

Cancers are groups of abnormal cancer cells. As cancer grows, some cells break off from the main cancer and spread to other parts of the body via the blood or lymphatic fluid. When cancer cells spread via lymphatic fluid, they get stuck in lymph nodes as immune cells try to filter them out. Then these lymph nodes swell.

Lymph nodes closest to the main cancer swell first. For example, breast cancer often spreads to lymph nodes in the armpit first. Generally speaking, the more lymph nodes with cancer cells in them, the more advanced the cancer.

Of note, certain kinds of cancers don’t spread to the lymph nodes but start in the lymph nodes themselves. These are called “lymphomas.” 

What is cancer staging?

Cancer stage determines how advanced your cancer is and which treatment options are best. Staging describes the:

• Size of the cancer

• Location of the cancer

• Where and how far the cancer has spread

• What the cancer cells look like

A lower stage means that the cancer is less severe with less spread. A higher stage means the cancer is more severe with more spread. Stages range from 0 to 4.

For example, a breast cancer that is only in the breast is stage 0 or 1. If breast cancer spreads to the lymph nodes, it may be stage 2 or 3. If the breast cancer spreads to another organ, like the liver, it’s stage 4. 

To figure out the cancer stage, your provider may order imaging tests or recommend a procedure to check lymph nodes. 

A CT scan or MRI can check for swollen lymph nodes that aren’t obvious on your physical exam. 

A lymph node biopsy can confirm if there are cancer cells in the swollen lymph nodes. This is a minor surgical procedure where a provider removes the lymph node from the body and then uses a microscope to look for cancer cells. Sometimes people need a surgery that removes the tumor and lymph nodes to determine the stage. 

What is TNM staging?

TNM staging is the most common system for cancer staging. It’s a more detailed way of describing how advanced cancer is. The letters stand for:

• T: tumor size (of the main cancer) 

• N: number of lymph nodes nearby where cancer has spread

• M: metastasis (spread) of the main cancer to other organs in the body

In the TNM system, there are numbers after each letter that give more details about the cancer. 

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined her interests in clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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