Swelling after COVID-19 shots may cause cancer false alarms

Anyone getting a mammogram or other cancer check soon after a COVID-19 vaccine should alert doctors, to prevent false alarms from a side effect

“We need to get the word out,” said Dr. Melissa Chen, a radiologist at the MD Anderson Cancer Center in Houston who recently had to reassure a frightened patient who sought cancer testing because of an enlarged lymph node.

An expert panel from three cancer centers -- MD Anderson, New York's Memorial Sloan Kettering and Boston's Dana-Farber -- published recommendations in the journal Radiology last week on how to handle scans complicated by the side effect.

The main message: “This should not prevent patients from getting the vaccine,” stressed Chen, one of the coauthors.

The nodes most commonly affected are in the armpit and near the collarbone, on the same side as the vaccination, Chen said.

It’s not clear how often it happens. The FDA found 16% of participants in the Moderna study reported some underarm swelling after their second dose. But if the lymph nodes are only slightly enlarged, they may show up on a medical scan without people noticing any bumps.

The consumer advice still is evolving. Where experts agree: If you’ve recently been vaccinated, tell the radiologist before any scan. That will help them evaluate if an enlarged lymph node is probably vaccine-related and can simply be monitored, or if it's worrisome enough for a biopsy or other test.

And try to schedule an upcoming screening or other cancer-related scan ahead of vaccination if it’s possible without losing your place in the vaccine line, the Radiology panel said.

People with active cancer that’s on one side of the body can choose vaccination on the opposite side to minimize confusion.

Don’t delay any urgent exams, radiologists stress. But there's some disagreement about non-urgent scans. The Radiology panel said to consider scheduling purely routine screenings six weeks after vaccination. In contrast, recommendations from Massachusetts General Hospital urge handling the side effect with good communication rather than delayed screening.


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

Top Stories

Top Stories

Top Stories

Top Stories

ABC News Live

ABC News Live

24/7 coverage of breaking news and live events