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COVID-19 vaccine side effect causing false positive cancer screenings

According to the MD Anderson Cancer Center, swelling caused by the COVID vaccine is causing false positives on cancer screening exams.

HOUSTON — One side effect of the COVID-19 vaccine is swelling.

RELATED: Houston expands who can get on COVID vaccine waitlist for FEMA location and other sites

According to MD Anderson Cancer Center, that swelling is causing false positives on cancer screening exams.

"Cancer experts at MD Anderson are seeing an uptick in mammograms identifying a false positive for breast cancer due to a common side effect of the available COVID-19 vaccines — swollen lymph nodes. The detection of swollen lymph nodes in imaging exams has led to false positives for leukemia and lymphoma patients, as well," MD Anderson said in a release.

MD Anderson experts said the swelling can impact results up to six weeks after vaccination. They're raising awareness of the issue so patients can plan accordingly.

Patients, except for women who are overdue for their screening exams, are being advised to wait six to 10 weeks after receiving the COVID-19 vaccine to schedule their exams.

Dr. Jessica Leung is Deputy Chair of Breast Imaging at MD Anderson. She said a lot of women are getting COVID vaccines now and they see “on an average week, perhaps five to 10 cases” of false positives.

The false positives have even resulted in biopsies being done.

“We have done biopsies to make sure it is not cancer. That was relatively early on in our experience, a few weeks ago,” she said.

Now, doctors are paying better attention to whether a patient recently had a COVID vaccine.

Leung said the new Johnson & Johnson vaccine uses a different technology than previous Moderna and Pfizer drugs and could possibly result in a different immune response.

"That will be interesting to see,” she said.

This was also the topic of a VERIFY report by KHOU 11's sister station, WUSA-TV in Washington D.C.


Should you plan a breast exam around your COVID-19 vaccine?


  • Dr. Lisa Mullen, Assistant Professor of Radiology at Johns Hopkins University
  • Dr. LaTasha Perkins, Physician and Professor at Georgetown University
  • The Society of Breast Imaging.


Yes. The vaccines can cause swollen lymph nodes in some people. When your radiologist sees a swollen lymph node during a mammogram, that can be a cause for concern and warrants a follow-up exam. Experts are trying to avoid false positives and unnecessary anxiety.

They suggest either scheduling your mammogram before your vaccine, or, as M.D. Anderson suggests, four to six weeks after your second dose. 


Your lymph nodes are like a home for your white blood cells. When those cells are working to fight off an infection, it can sometimes cause the nodes to enlarge. That's what happens to some people after receiving vaccines, according to Dr. LaTasha Perkins.

"You see it a lot and when you're being vaccinated for a virus like the flu or COVID-19, but you also can see it when you get vaccinated for HPV or a tetanus shot," she said. "The swollen lymph nodes are not a cause for concern, because it shows that your body is mounting an immune response. That's exactly what we want it to do when you get a vaccination."

Radiologist Dr. Lisa Mullen says that is also what happens when your body is fighting off something more nefarious, like cancer. Benign flare-ups can make her job of identifying breast cancer much more difficult.

"When we started seeing patients who had had the COVID vaccine," she says, "We were noticing that they had larger than usual lymph nodes on the side where they had been vaccinated."

But before she knew if a patient had been vaccinated, this looked like a cause for concern — one which requires recalls, follow-up exams and possibly biopsies. 


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