Covid vaccine-induced swelling can lead to false cancer diagnosis, doctors warn

Cancer experts and radiologists in the US are warning Covid-19 vaccine recipients that an otherwise normal immune response can be mistaken for cancer if it appears on a mammogram or other cancer screening.

Prior to major offensives against infections and unwanted intruders, some of the body's defense forces, the white blood cells, gather in lymph nodes. However, lymph nodes, especially in the armpit, can swell up following Covid-19 vaccinations. 

As cancer screenings continue parallel to vaccination drives across the world, a scan conducted soon after vaccination may yield a false positive and cause unnecessary stress during an already challenging time. 

“This should not prevent patients from getting the vaccine,” says Dr. Melissa Chen, a radiologist at the MD Anderson Cancer Center in Houston.

Chen and colleagues at MD Anderson, New York's Memorial Sloan Kettering and Boston's Dana-Farber formed a panel to sound the alarm about the potential for false positives amid the vaccine rollout. 

The panel has warned medical experts to prepare for unusually “large volumes” of chest computed tomography (CT) scans, positron emission tomography (PET) scans and mammograms showing swollen lymph nodes as vaccination drives continue.

The lymph nodes most commonly affected are located near the armpit and collarbone on the side that patients receive their vaccine. 

The extent to which this swelling happens is not fully understood, and has been reported in studies on recipients of the Pfizer/BioNtech and Moderna vaccines but not the Johnson & Johnson vaccine. 

The resounding advice is for patients to tell their radiologist that they've been vaccinated prior to a scan so that any swelling in the lymph nodes doesn't necessarily result in misdiagnosis or trigger unnecessary, costly and potentially invasive procedures.

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