Among the many potential lingering side effects of breast cancer, one of the most challenging can be lymphedema, a condition in which lymphatic fluid gets trapped in lymph vessels and causes swelling.

“It’s a complication that can happen over time,” says Nusayba Bagegni, MD, an oncologist and an assistant professor of medicine at Washington University School of Medicine in St. Louis. “Women need to be mindful of this from the get-go.” Between 5 and 40 percent of women who have had breast cancer surgery may experience lymphedema following their surgery, according to BreastCancer.org.

How it happens: Lymphedema occurs when the drainage of bacteria-filtering lymphatic fluid — a clear or white fluid made up of infection fighting white blood cells — is disrupted, causing fluid to build up in the surrounding tissues.

Here’s what you need to know about lymphedema, its triggers, and how you can get it treated.

The Top Causes of Lymphedema

Cancer

One of the most common reasons lymphedema occurs is the tumor itself. Specifically, if a cancerous tumor is too big — and is growing near a lymph node or a lymph vessel — it can block the flow of lymph through the network of vessels it normally flows through.

Surgery

During breast cancer surgery, doctors often remove lymph nodes under the arm and near the collarbone, because that’s the pathway through which the cancer can spread. After the surgery, pathologists examine the nodes for signs of cancer. Staging and treatment plans will depend, in part, on if and how many nodes are affected.

Typically, surgeons decide how many lymph nodes to remove depending on whether you have enlarged lymph nodes, as well as how big your breast tumor is. In the past, many nodes were routinely taken out. These days, techniques have been refined, and surgeons can take fewer. However, there is a chance you will develop lymphedema even if just one lymph node is removed.

Radiation Therapy

Radiation therapy can cause scarring, inflammation, and damage to the lymph nodes or lymph vessels, which can block the flow of lymph. It does not, however, necessarily happen directly after radiation is received. For instance, lymphedema can occur anywhere from 1 to 24 months after your radiation therapy is complete. In some cases, it may abate over time.

Signs You May Be Developing Lymphedema

“It’s important to note that women may experience lymphedema in the breast itself as well as in the armpits due to radiation,” Dr. Bagegni says. “We know a patient has breast lymphedema when there’s asymmetry and swelling within the breast itself as well as in the surrounding areas.”

Other signs to watch for, according to Johns Hopkins Medicine:

Swelling in the arm or hand, particularly on the side where lymph nodes were removed
A feeling of heaviness or tightness in the arm, armpit, or chest
Pain or weakness in the arm
Trouble moving a joint, particularly in the arm
Changes or thickening of the skin

What to Do

If you think you're developing lymphedema, you should contact your doctor as soon as possible. One reason doctors want you to act promptly is that lymphedema can increase risk of skin infection, such as cellulitis. You’ll know you have a skin infection if your skin becomes swollen, red, or warm to the touch.

“This happens because trapped fluid that cannot drain can prompt germs,” says Paula Rosenblatt, MD, a medical oncologist at the University of Maryland Greenebaum Comprehensive Cancer Center in Baltimore. “Any injury or skin puncture to the arm can also lead to infection.”

How It’s Treated

If you develop lymphedema, it’s likely your healthcare provider will suggest you wear a compression sleeve that helps maintain blood flow and reduces discomfort and swelling. In more severe cases, you may need a pneumatic pump, a device which secures to your body and uses compressed air to apply pressure and force lymph fluid out of the limb.

In addition, your healthcare provider may connect you with a lymphatic specialist who can work with you and a physical therapist to provide manual lymphatic drainage, exercises, and instructions on self-massage. Yoga, tai chi, pilates, cycling, and swimming may help, too.

“We also encourage patients to maintain an ideal body weight, or lose weight, as obesity can be a risk factor for lymphedema,” Dr. Rosenblatt says.

Finally, make sure to be monitored routinely, avoid skin punctures and, if you need bloodwork or blood pressure readings, ask for those to be done on the non-lymphedema arm.

Ultimately, lymphedema can end up being a lifelong health issue, even if it doesn’t happen right away.

“If it’s significant, it can be a chronic problem that causes heaviness and a lot of discomfort,” Bagegni says. “However, our hope is that over the years, as we do fewer invasive procedures, we will see fewer and fewer cases of lymphedema.”

Breast Cancer and Lymphedema: What It Is, Why It Happens, and How It’s Treated