During the course of breast cancer diagnosis and treatment, lymph nodes near the breasts can become enlarged. According to data from the Centers for Disease Control and Prevention (CDC), one in four female breast cancers spread to the lymph nodes, but cancer spread is not the only reason for lymph node swelling (also known as lymphadenopathy).

Whatever the cause, swollen lymph nodes can raise a multitude of questions when you have breast cancer. It’s important to know what else could be causing this symptom, and to check in with your healthcare provider so they can help you get to the bottom of it.

Lymph Nodes and What They Do

The lymphatic (or lymph) system is an essential part of the immune system and is made up of a network of lymph nodes and lymphatic vessels, according to the American Cancer Society (ACS). These look similar to blood vessels, but instead of blood, they contain a clear, watery substance called lymphatic fluid.

“Lymph nodes act as filters for lymphatic fluid, which carries waste products, foreign substances, and immune cells throughout our body. They are essential because they help detect and fight infections and diseases, including breast cancer,” says Corey Speers, MD, PhD, radiation oncologist at University Hospitals Cleveland Medical Center and member of the developmental therapeutics program at the Case Comprehensive Cancer Center (CCCC).

The lymphatic system also helps drain away toxins through the lymph fluid. When breast cancer treatment involves removal of axillary lymph nodes (lymph nodes under the arm), lymphatic fluid can get backed up in the affected upper extremity area and cause generalized swelling called lymphedema, according to the ACS. A study published in 2020 in the Journal of Clinical Oncology found that most people experienced lymphedema between 12 and 30 months after a mastectomy or lumpectomy.

I Have Breast Cancer: Should I Be Concerned if My Lymph Nodes Are Swollen?

Normally, lymph nodes are less than one centimeter in diameter — about the size of an uncooked bean — although nodes in the chest can be even smaller, according to StatPearls.

“Swollen lymph nodes can be a sign that breast cancer has spread to those nodes. When cancer cells break away from a tumor in the breast, they can travel to nearby lymph nodes through the lymphatic system,” Dr. Speers says. “However, it's important to note that not all swollen lymph nodes are due to cancer. They can also become enlarged because of infections, other medical conditions, or even physical injury.”

Some vaccinations — like the jab for COVID-19 — can cause temporary lymph node swelling, according to a study published in the European Journal of Radiology in 2022. Even something as simple as a cold or flu can cause swollen lymph nodes, notes Cleveland Clinic.

Your provider can learn important clues about what’s causing a swollen lymph node by identifying specific symptoms. For example, a painful node that is easy to move under the skin may point to infection versus metastasis, according to StatPearls. On the other hand, a firm, painless, immobile node is more likely a sign that cancer has spread.

When to Contact Your Healthcare Provider

When you have breast cancer, there is no wrong reason to contact your healthcare provider. Even if a swollen lymph node has nothing to do with cancer, they will still want to know about it. According to Speers, you should contact your provider if you notice:

Swelling or a lump in the area near your breast, underarm, or collarbone that doesn’t go away after a few weeks
Pain or tenderness in the lymph nodes
A sudden increase in size or number of lymph nodes you can feel
Any other unusual or persistent symptoms

“If you have any concerns, it is always best to consult your healthcare provider to get a proper evaluation,” Speers says.

Your provider may want you to have a biopsy of the swollen node to check for cancer cells, according to the ACS. The results of a biopsy can give you and your health team a clear picture of why your lymph node is swollen and can direct your care going forward.

How to Treat Swollen Lymph Nodes

“Treatment for swollen lymph nodes depends on the cause,” Speers says. “If the swelling is due to breast cancer spread, treatment might involve surgery to remove the affected lymph nodes.”

According to the American Cancer Society, breast cancer that has spread to the lymph nodes can also be treated with:

Chemotherapy
Hormone therapy
Immunotherapy
Radiation therapy
Surgery
Targeted medications

If your biopsy comes back negative, your lymph node may be swollen for another reason. “If the swelling is due to an infection, your doctor may prescribe antibiotics or other medications,” Speers says.

“Other noncancerous causes of swollen lymph nodes may respond to over-the-counter pain relievers and warm compresses can help reduce pain and swelling. It's essential to address the root cause of the swelling, so always consult with your healthcare provider for a proper diagnosis and treatment plan.”