Normal immune response to the COVID-19 vaccine can mimic a sign of breast cancer

Doctors recommend patients schedule their mammogram before receiving a COVID-19 vaccine, or space out the two appointments, after some women have been mistaking swollen lymph nodes for breast lumps.

These swollen lymph nodes, which are a side effect of the COVID-19 vaccine, can also show up in mammograms and other types of imaging scans, experts say.

“There have been a couple of situations where the patient went for a mammogram and on the mammogram, there it was,” said Dr. Harold Burstein, a breast oncologist at Dana-Farber Cancer Institute.

Lymph nodes are specialized tissue in the body's immune system that contain white blood cells and help fight against infection and disease, according to the National Cancer Institute. They're normally the size of a lima bean and are all over the body, Burstein said, but the most prominent lymph nodes are located in the armpits, neck and groin area.

The ones located under the armpits are most likely to swell after vaccination because they’re closest to the injection site. They could begin swelling as soon as a few days after vaccination and could last as long as 12 weeks. Additionally, the vaccine shouldn’t create any abnormalities in the breast itself, only under the armpit.

But health experts emphasize this is completely normal as increased inflammation suggests antibodies are at work protecting the body against SARS-CoV-2, the virus that causes COVID-19.

“This is a normal immune response to a potent vaccine,” Burstein said. “It’s to be expected. It’s a well-desired consequence of the vaccine.”

Other vaccines elicit a similar response, such as vaccines for influenza and the human papillomavirus. Some experts speculate this may be happening more frequently as more people get vaccinated against COVID-19 at the same time.

The two mRNA vaccines that are authorized for the disease are highly effective. They have been known to evoke other side effects like low-grade fever, chills, headaches and fatigue.

It's possible the potent mRNA vaccines are causing swollen lymph nodes at a higher rate than other vaccines as they appear to cause more side effects, said Dr. Jessica Leung, professor of diagnostic radiology and deputy chair of breast imaging at the University of Texas MD Anderson Cancer Center.

“But with the non-mRNA vaccines (like Johnson & Johnson), it’ll be interesting and educational to see what happens," she said.

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Even though swollen lymph nodes could mimic a concerning lump during a self-exam or mammogram, it’s still important to get both the COVID-19 vaccine and screened for breast cancer, Leung said.

To avoid confusion, she recommends getting screened before getting vaccinated. If that’s not possible, MD Anderson Cancer Center guidelines say to wait around four to six weeks after receiving the vaccine.

“Don’t wait too much longer after six weeks,” Leung said. If it’s not possible to reschedule your mammogram, “get your mammogram anyways, but let your providers know (you’ve) had the COVID vaccine in this arm, at this date.”

Most providers can tell the difference between a swollen lymph node and something that is worth concern, especially if they know the patient had been vaccinated against COVID-19 in the recent weeks.

Leung and Burstein know how difficult it is to get a COVID-19 vaccine as supply is still limited, so they advise against rescheduling your appointment to get vaccinated.

“(But) don’t forget your mammogram even with this because cancer is still a big problem in this country and this is a test ... that can potentially save a woman’s life from breast cancer,” Leung said.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

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This article originally appeared on USA TODAY: COVID-19 vaccine: Side effect can mimic breast cancer in mammogram