SAN FRANCISCO (KPIX 5) – In a growing number of women, a COVID-19 vaccine is causing some to think they may have breast cancer. But top doctors in the Bay Area say it may actually be a side effect of the shot.

“And I could see a bump, a swelling,” recounted Bay Area Veterinarian Dr. Emilie Ravn.

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After getting vaccinated, Ravn noticed a small lump in her armpit. “I did think to myself, should I reach out to my doctor?” she recalled.

Ravn is far from alone.

“We have definitely seen this at UCSF,” commented Dr. Bonnie Joe, who is chief of breast imaging at the medical center.

What Joe and her team are seeing on mammograms are enlarged lymph nodes in some recently COVID-19 vaccinated women.

“We now are starting to see patients who are presenting for their screening mammogram and then incidentally they have enlarged lymph nodes and we’ve noticed that these nodes are on the same side where they got vaccinated,” explained Dr. Joe.

A mammogram of a recently vaccinated woman showing a swollen lymph node. (UCSF)

A mammogram of a recently vaccinated woman showing a swollen lymph node. (UCSF)

With COVID-19 vaccinations picking up steam around the Bay Area, doctors are seeing more cases of lumps under armpits or near collarbones.

Absent a COVID shot, swollen nodes near the breast can be a red flag.

“So that’s the sign of more aggressive or serious disease,” said Dr. Laura Esserman, director of the Carol Franc Buck Breast Care Center at UCSF, and a breast cancer surgeon.

But in recently vaccinated women, tests reveal these bumps are not cancers. They’re just swollen glands.

For many, it can cause unnecessary anxiety.

“Most people are being called back for these things and I think that’s a problem. Because it’s very scary and a bunch of people are going to get biopsies that they don’t need,” said Esserman.

The cost can be daunting.

“Some of these tests are incredibly expensive. Now if you really need it, you should do it. But if you don’t need it the co-pays can be $1,000, more than $1,000. And people need to be told that this can happen,” cautioned Esserman.

You may ask as to why these lymph nodes swell after getting vaccinated?

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Experts explain that it’s a good sign the vaccine and your immune system is working.

“Your lymph nodes are the factories for making those antibodies,” Esserman explained.

Swollen lymph nodes are also an expected side effect. In clinical trials, 11.6% of those who received a first dose of the Moderna vaccine experienced a swollen lymph node. That number increased to 16% after the second dose.

And while the rates were lower with the Pfizer COVID-19 vaccine, Esserman and others believe that real rates for both the Moderna and Pfizer vaccines may actually be much higher.

The question for doctors and patients: what do you do with that information?

“So, we want to be careful not to overreact to that information. We don’t want to miss a clinically important finding.  But I think it’s all confounded by the vaccine,” Esserman said.

An expert panel of radiologists has now weighed in with the latest publication of journal “Radiology”

Their advice: if you’re due for a routine screening, consider postponing your mammogram for at least 6 weeks after the last dose of the vaccine. But if you have an urgent reason to get a screening, for example symptoms, don’t delay.

There’s also good news. If you’re not yet eligible to get a COVID-19 vaccine, now is the perfect time to get your mammogram. By all accounts, it’s a lot easier to schedule than the shot at the moment.

“We are recommending that women who are due for their screening mammogram don’t wait. It’s safe to come in and get that mammogram done,” said Dr. Joe.

As for Dr. Ravn, as a vet, she knows how vaccines can results in swollen lymph nodes in her furry patients. Even so, when it happens to you, close to your breast, it can cause anxiety.

She is reassured by the information about the COVID-19 vaccine side effect, and believes knowledge is power.

“It’s important for everyone to kind of be aware of things and if you’re worried to discuss it with your doctor,” said Ravn.

If the lump lasts for more than 6 weeks after vaccination, let your doctor or health care professional know.

And, if you are getting a mammogram, and you just received the COVID-19 vaccine, make sure to tell the radiologist that you were vaccinated and on what arm.

Esserman and her team said they are committed to find the best way to screen for breast cancers.   She told KPIX 5 that the pandemic highlights the importance of understanding an individual’s risk.

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If you undergo breast cancer screening, you can help researchers and Esserman by signing up for the Wisdom Trial.