Don’t Be Alarmed by This COVID-19 Vaccine Side Effect That Could Be Confused With Breast Cancer

Our expert explains why swollen lymph nodes happen
covid vaccine swollen lymph nodes

As more people across the globe continue to receive the COVID-19 vaccine, we’re learning more about certain side effects that the vaccine can cause.

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And one side effect — swollen lymph nodes under the arms — has been getting more notice because of the serious disease it overlaps with: breast cancer.

To better understand what’s causing this symptom and what you should know before getting your COVID-19 vaccine, we talked to diagnostic radiologist Laura Dean, MD.

Why does the COVID-19 vaccine cause lymph nodes to swell?

Lymph nodes are part of the body’s immune system so, according to Dr. Dean, swollen lymph nodes are a potential side effect of any vaccine. “The whole point of the vaccine is to get your immune system to mount a response to whatever the vaccine agent is,” she says.

But it seems that the new COVID-19 vaccine is causing a more robust swelling in lymph nodes. And those swollen lymph nodes, like other side effects, vary from person to person. “We’re still learning about these vaccines and the side effects as more and more people receive them,” Dr. Dean says.

The swollen lymph nodes generally appear a few days after someone receives the vaccine, on the same side of the body as they got the shot. “We’re still watching these examples but right now we think that symptom subsides with a few days to a few weeks,” she adds.

Swollen lymph nodes can also be a sign of breast cancer

It’s the location of the lymph nodes involved with this particular side effect that’s causing concern. Many times (but not always) the location of a person’s lymph node swelling corresponds to the site of infection. For many breast cancer patients, that includes the lymph nodes in the armpits.

“If breast cancer moves outside of the breasts, it tends to go to those lymph nodes under the arms because that’s the natural drainage pattern of the lymph fluid inside the breast tissue,” Dr. Dean explains. “It’s a very integrated system, so it’s one of the areas we closely scrutinize.”

Because early detection is so key to treating breast cancer, it’s understandable that this overlapping symptom is causing a little bit of confusion and even alarm in many patients.

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What else could swollen lymph nodes mean?

It’s important to remember that although swollen lymph nodes are one potential sign of cancer, they can have a number of other causes. And while the COVID-19 vaccine appears to only cause swelling on one side, swelling in lymph nodes on both sides of the body is also not necessarily a sign of cancer.

“You see general lymph node enlargement — under the arms, in the chest or groin — with something like lymphoma,” says Dr. Dean. “But there are other reasons you’d see that, too, which are far less serious than cancer.”

Other causes of swollen lymph nodes include:

There are other conditions, too, that Dr. Dean says healthcare providers may look into. “We address the issue by taking a very detailed patient history and looking for other conditions that may cause the swelling like rheumatoid arthritis, lupus or autoimmune diseases.”

And, yes, this includes swelling on just one side. “We don’t want to miss something because a lymph node on just one side is swollen,” she adds. “But we’ve also added questions about recent COVID-19 vaccines to our screening questions to make sure we’re getting a full view of what might be affecting the patient.”

Keep up with your preventive care plan

The most important thing, Dr. Dean says, is that patients maintain their preventive care plan for breast cancer, especially mammogram screenings.

Just as healthcare providers have worked to ensure a safe environment for keeping such appointments throughout the pandemic, so, too, are they adapting care plans to account for this particular vaccine side effect.

“We’re now including questions about the vaccine — how many doses have you had and in which arm — in our pre-appointment screening questions for patients,” Dr. Dean says. “And we’re also adapting our mammogram appoint scheduling to allow for some flexibility with more patients now receiving the COVID-19 vaccine.”

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The Society of Breast Imaging recommends scheduling your mammogram either before your first dose of the COVID-19 vaccine or about four to six weeks following your second dose, if possible. If that’s not possible, though, it’s important to keep both your scheduled screening and your vaccine appointment.

“It’s important that patients maintain their scheduled mammograms,” she says, “but it’s also important that they receive their COVID-19 vaccination. One shouldn’t be canceled because of the other. If you have a mammogram screening shortly after one of your vaccinations, your healthcare provider will document that and take it into account.”

“We’ll work with you to explain what’s going on, what we see and what might be a side effect,” she adds. “And if there’s potential overlap, you can schedule a short-term follow-up screening for a few weeks later just to be safe.”

The bottom line

Again, Dr. Dean stresses that there’s no reason to be alarmed about getting swollen lymph nodes from the COVID-19 vaccine. “This type of reactive change that we’re seeing with the COVID-19 vaccine is exactly what we should see,” she says. “It’s your body mounting the immune response as it’s supposed.

While those enlarged lymph nodes may be worrisome, she adds that healthcare providers are aware and monitoring them in patients. “We’re keeping an eye on this side effect and when it comes to your mammogram screening, we’re ready to explore any abnormalities in that context.”

Finally, she reiterates how important it is to maintain your preventative care appointments despite these side effects. “It’s extremely important COVID-19 vaccinations continue. And it’s also important to know that we’ll never turn any patient away from a mammogram screening for getting their vaccination. We’re armed with as much information as possible and we’ll work with every patient to make sure they get the care they need.”

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