In early 2021, a team of Penn Medicine radiologists began to notice a rise in axillary lymphadenopathy (swollen lymph nodes in the armpits) on multiple types of breast imaging (mammography, ultrasound and MRI).
Axillary lymphadenopathy can be a sign of breast cancer. In most of the women, though, the swelling subsided within weeks. Subsequent tests and scans showed no evidence of breast cancer.
Good news, ultimately – but why was this happening? Why the sudden rise in enlarged lymph nodes in the arm pit?
“We suspected a correlation between these abnormal mammograms and the COVID-19 vaccine, but didn't know for sure,” says Christine Edmonds, MD, breast radiologist at the Hospital of the University of Pennsylvania (HUP).
Dr. Edmonds and her team started digging. They reached out and asked the women whether they’d received the COVID vaccine (information that wasn’t necessarily in their medical records), when they received it, and in which arm. Again and again, women reported that they had been vaccinated in the weeks prior to their abnormal mammograms.
Clinicians nationwide were reporting similar findings.
What We Now Know
Enlargement of lymph nodes in the armpit is a normal reaction to the COVID vaccine, and nothing to worry about. When seen on mammograms, the enlarged nodes related to the vaccine have the potential to be mistaken for signs of breast cancer or other diseases such as lymphoma. The enlarged nodes may cause additional testing, sometimes even biopsies – and therefore, unnecessary stress and anxiety.
“We perform successful breast biopsies every day, but like any procedure involving a needle, it comes with risk,” Dr. Edmonds says. “So before we biopsy, we want to make sure that risk is justified. Just as importantly, a false positive on a mammogram can induce anxiety in patients and other hassles: Worry, scheduling and attending appointments, biopsy discomfort, the wait for results. We don’t want women to experience any of these things unnecessarily.”
The American Journal of Roentgenology published the Penn Medicine team’s findings in February 2021. Within weeks, the Society of Breast Imaging (SBI), a leading breast imaging organization, began encouraging most women to wait four to six weeks from the date of their last COVID vaccine or booster to undergo routine, screening mammograms in efforts to avoid such false positives. Recommendations are different for women considered high-risk, and for women whose screenings or care are already delayed.
“Above all, we want women everywhere to be aware of this so that they get the best possible breast imaging care,” explains Emily Conant, MD, Division Chief of Breast Imaging at the Perelman Center for Advanced Medicine, one of the paper’s authors, and Vice President of the Society of Breast Imaging.
First Fact First
The words “COVID vaccine” and “mammogram” in the same sentence can be scary! Before we discuss SBI’s mammogram guidelines in more detail, let us stress:
The COVID-19 vaccines and boosters do not cause breast cancer.
The COVID vaccine and subsequent boosters continue to protect against COVID with impressive efficacy. Its adverse events (better known as side effects) are limited almost exclusively to manageable and temporary pain and discomfort. While lymph node swelling experienced by some women post-vaccine can be misinterpreted as cancer, it is not cancer. Quite the opposite, actually: Swelling after the COVID vaccine or booster can actually be considered good.
“How Is Swelling Good?”
Axillary lymphadenopathy is evidence that the COVID vaccine is doing its job by causing a response in your immune system.
“Lymph node swelling following the COVID-19 vaccine isn’t even technically an adverse response,” Dr. Edmonds explains. “It’s simply a response.”
Lymph nodes are tiny organs of the lymphatic system that filter foreign particles. Most of us have about twenty of them in each armpit. When we get sick, whether from a cold or cancer, they become inflamed or enlarged.
Because the COVID vaccine stimulates the immune system, a similar response can take place when the vaccine particle enters the body. It’s called an immunogenic reaction. Immunogenic reactions are heightened with the COVID vaccine likely in part because the COVID-19 vaccine usually enters the body close to the armpits – and because lymph nodes are some of the immune system’s first responders.
“Axillary lymphadenopathy following the COVID-19 vaccine is a good thing,” Dr. Conant stresses. “It means you're responding. We just don't want to confuse it with a bad thing.”
“So When Should I Get My Preventative Mammogram?”
Back to those recommendations from the Society for Breast Imaging.
If you aren’t high-risk, and if your regular screening mammograms are on schedule: Schedule (or reschedule) your next routine screening mammogram before your next COVID-19 vaccine dose or at least 4-6 weeks after. This reduces the chance that vaccine-induced swelling might appear on your mammogram.
However, if you have concerning symptoms like a breast lump or thickening, are considered high-risk for developing breast cancer, have known breast cancer, or if you’re overdue for a mammogram: Proceed with your COVID-19 vaccine and mammogram as planned, but let your mammogram scheduler and technician know if you were recently vaccinated.
No one should reschedule their COVID booster. The COVID vaccine and boosters are critical to stopping the spread of the virus – don’t delay it. Similarly, no one should delay their mammogram for any longer than absolutely necessary.
“What Should I Tell My Tech?”
Penn Medicine breast imaging schedulers now ask patients about their COVID vaccine history when scheduling their appointment. You’ll be asked again when you arrive for your mammogram.
“This information is added to the chart where we, the radiologist, see it,” Dr. Edmonds explains.
If your imaging practice doesn’t ask about your COVID-19 history, offer the information anyway. Simply tell your mammography technologist that you recently received a COVID booster – the date, and in which arm – and ask them to add it to your chart and records. Clarify whether it was your first or second dose or if you just received a booster. This information will help the breast radiologist accurately interpret your mammogram.
Above All – Don’t Delay!
Too many women have already delayed their mammograms and routine cancer screenings during the pandemic.
"Back in Spring of 2020, as we were getting a handle on COVID, patients were initially told not to come in for their screening mammograms,” Dr. Edmonds says. “It wasn’t long before we realized that medical settings are actually very safe. But some patients are still afraid to come in for routine studies. Unfortunately, we’re seeing the results of that in the form of more advanced cancer.”
For more information on the technology behind the COVID-19 vaccine, visit out mRNA vaccines page.