The COVID-19 vaccine has a side effect that is being mistaken for breast cancer

Women are scheduling biopsies over the discovery of a vaccine symptom that usually indicates breast cancer

By Nicole Karlis

Senior Writer

Published March 3, 2021 2:52PM (EST)

Doctor examining scan (Getty Images)
Doctor examining scan (Getty Images)

The SARS-CoV-2 vaccine is causing an unexpected side effect in many patients, leading many women to believe that they may have cancer and even scheduling biopsies.

The observation of swollen lymph nodes in one's armpits is a common sign of breast cancer, particularly in female patients. Swollen lymph nodes can also be a side effect of viral infections, and certain flus; an immune response, such as that which the body experiences after vaccination, appears to be the cause of said swollen lymph nodes. According to CNN, radiologists have seen an uptick in concerned patients which has led to a rush of biopsies.

To be clear, the COVID-19 is not causing breast cancer, but in some cases it is causing lymph nodes to swell which is worrying many women. Worse, some women have even reported seeing white "blobs" in their regular mammograms, which are a more serious sign of cancer. Yet such blobs are actually a COVID-19 vaccine side effect, too. 

Doctors emphasize that this is an expected and normal possible side effect, as the white a reaction by the immune system to the vaccine. It occurs on the same side as the arm where the person received the vaccine shot.

"When you hear hoofbeats, don't think zebra," Dr. Connie Lehman, chief of breast imaging in Massachusetts General's department of radiology, told CNN. "If a woman had a vaccine in the arm on the same side, and the lymph nodes are swollen, this is a normal biological response. It's totally expected. It just doesn't make sense to start imaging."

During clinical trials, an estimated 16 percent of patients reported swollen lymph nodes after the second inoculation of the Moderna vaccine; 11.6 percent reported swollen lymph nodes after the first dose. For the Pfizer vaccine, only 0.3 percent of patients in trials reported it. In a Food and Drug Administration (FDA) briefing document for the Johnson & Johnson vaccine, swollen lymph nodes aren't listed as a reported side effect.

In a recently published retrospective study in the American Journal of Roentgenology, a researcher at the University of California–Los Angeles found that 23 women had swollen lymph nodes appear on breast imaging after receiving the COVID-19 vaccine; 13 percent were symptomatic, and 43 percent were detected on diagnostic imaging.

Understandably, doctors are eager to spread the word that this might happen — and it's not a reason to freak out.

"I am particularly eager to get the word out to all the patients undergoing surveillance after successful prior treatment of cancer," Lehman told The New York Times. "I can't imagine the anxiety of getting the scan and hearing, 'We found a node that is large. We don't think it's cancer but can't tell,' or worse, 'We think it might be cancer.'"

Due to the nuance of the symptoms, some professional groups like the Society of Breast Imaging are advising that medical professionals consider asking about a patient's vaccination status, the date and which arm they received the vaccine, in an intake form. The group also advises women to schedule screening exams prior to the first dose of the vaccine, or four to six weeks after the second dose of either the Pfizer or Moderna vaccines. The Society of Breast Imaging states that if the swollen area continues after a short-term follow-up with a patient's physician that a biopsy should be considered. They also advise that if the lump persists for six weeks after one's vaccination to let your healthcare provider know.

By Nicole Karlis

Nicole Karlis is a senior writer at Salon, specializing in health and science. Tweet her @nicolekarlis.

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