Reading: Can a Recent COVID Vaccine Affect Your Mammography Results?

If you’re like me, and you’ve put off your preventive health exams until after COVID vaccination, there’s something you should know before you schedule your next breast imaging exam. A common side effect of the vaccine can be misinterpreted as cancer on a mammogram. 

Many women experience swelling in the armpit on the side where they received their injection. According to the Centers for Disease Control, swelling or tenderness under the arm was reported in 11.6 percent of patients aged 18-64 following their first dose of Moderna, and 16 percent of patients in that age group following their second. (Swollen lymph nodes were also reported in about 1 percent of patients receiving the Pfizer vaccine, but researchers didn’t explicitly ask subjects about this symptom.) Typically, when mammograms show swollen lymph nodes on one side — a finding known as axillary adenopathy — radiologists conduct follow-up tests to rule out breast cancer.  

In order to allay undue anxiety — and prevent unnecessary follow-up diagnostic tests — the Society for Breast Imaging (SBI) recently issued special mammography guidelines for women receiving the COVID-19 vaccine. CoveyClub talked to SBI president Dr. Jessica W. T. Leung, MD, who is also professor of diagnostic radiology and deputy chair of breast imaging at University of Texas MD Anderson Cancer Center in Houston, about the new guidelines and the ideal timing for breast exams around the time of vaccination.

CoveyClub: Can you tell us about the Society for Breast Imaging’s new guidelines for women receiving the COVID-19 vaccine — and what prompted them? 

Dr. Leung: There were many anecdotal reports that radiologists were finding enlarged axillary lymph nodes (the axilla is the medical term for armpit) on mammograms in women who had recently been vaccinated. This is arguably a good sign — it says “my immune system is working” — and that’s what you want, to fight off the virus. But it can look similar to a tumor involving the lymph nodes. For that reason, we recommend that women either schedule their mammogram before their vaccination, or wait until four to six weeks after their last dose of the vaccine.

It’s really about the timing: If you have lymph node enlargement seen on a mammogram today, and you have your vaccine tomorrow, it’s impossible that it’s from the vaccine. Based on that logic, we would ideally want you to get your yearly mammogram before you get the vaccine. But I understand why women would want to get their vaccine first. If you’ve already started your vaccination, we suggest you wait a little while after you get your last dose of vaccination before getting your mammogram so that should you have enlargement of a lymph node from the vaccine, there is time for it to go back to the normal size. For most women, swelling dissipates in approximately four to six weeks. Not all women will have enlarged lymph nodes, some women will have lymph nodes that go away a lot sooner than four to six weeks, and some women can be swollen even longer, such as eight weeks. But with the four- to six-week guideline, we can catch the majority of women.  

CoveyClub: As you well know, it’s not always possible to orchestrate your medical appointments — and especially your COVID-19 vaccination dates — so that everything is perfectly aligned. If you do have a mammogram within a month or two of your COVID-19 vaccine, and your mammographer does not ask about your COVID-19 vaccine history, should you volunteer that information? 

Dr. Leung: Yes, life happens, and you can’t always schedule the way you want to, either because of the availability of appointments, jobs, or family obligations. Should that suggestion not be possible for whatever reason, it’s okay. You can get your vaccine and your mammogram. Just let your facility and your doctor — and your technologist and your radiologist — know about your history. They need to know that oh, this patient had a vaccine on this day, so what I’m seeing on the mammogram makes sense — lymph node swelling is probably due to the COVID vaccine. 

This is the information we suggest you provide: Tell them you had the COVID vaccine, tell them when you had the vaccine, and tell them in which arm. If you get injected in your left arm, swelling of the lymph nodes should be on the left side. There are always outliers, and it is possible to have swelling on the other side, but it’s much less likely. It’s also possible that swelling of the lymph node is not only under your arm but also in your neck. But the single most likely spot is on the same side in the armpit. 

CoveyClub: Do the new recommendations apply to women who are at high risk of breast cancer or who have already had breast cancer?

Dr. Leung: This recommendation is for the average population. I work at a cancer center, so some of our patients have genetic mutations, family histories, or may already have had breast cancer. So we may biopsy some of those patients if they have swollen lymph nodes, even if they have recently been vaccinated.  Women must be evaluated on a case-by-case basis. If you are unsure whether you should postpone an exam or are concerned about a lump or swelling, you should consult with your doctor.

CoveyClub: Can you explain, biologically speaking, why the lymph nodes would swell following vaccination? 

Dr. Leung: Lymph nodes are an important part of the immune system. To put it simplistically, lymph nodes are where antibodies are made to fight off infections. However, the lymphatic system is involved in a variety of processes in the body, and lymph nodes, which help to filter out “bad cells” in the body, can swell in response to infection, cancer, or inflammatory diseases like rheumatoid arthritis and sarcoidosis. So when a lymph node gets big, we don’t know, just by looking at the lymph node imaging, if it’s due to infection, inflammation, or the presence of a tumor. It’s the whole picture — including the patient’s medical history, her symptoms, and physical exam — that tells us what is going on.

What happens with the COVID-19 vaccine is that an inciting agent is injected into the arm, which causes an immune reaction and primes your immune system to fight off the COVID-19 virus, so you do not get as sick if you get infected. That’s the basic theory. We have lymph nodes all over our bodies, but the closest lymph nodes to the upper arm, where the vaccine is usually injected, are those in the axilla. When the vaccine is injected into the upper arm, the axillary lymph nodes on the side where you received your shot can respond to that. 

CoveyClub: Why do we see this lymph node swelling in response to the COVID-19 vaccine, and not as commonly in response to other types of vaccines like flu or HPV (human papillomavirus)? 

Dr. Leung: We don’t have the answer, mostly because we don’t even know how all the COVID-19 vaccines will perform at the moment. We are seeing it more compared to the flu or chickenpox vaccine, but we are comparing apples and oranges in the sense that so many more people are being vaccinated for COVID-19 in a relatively short period of time. Maybe it’s not really more, but because of this concentration of people getting vaccinated, it’s showing up more. 

CoveyClub: Because axillary adenopathy can be a sign of cancer or infection, should women still be mindful of this symptom and tell their doctor about it? Or only if it persists for more than four weeks? 

Dr. Leung: Making medical diagnoses is almost like putting together a puzzle, and the patient’s history is very important, as are her symptoms, and her old mammograms. When a doctor judges lymph node swelling, there are a variety of considerations: Is it hard, is it immobile, is it getting bigger? But it’s always on a case-to-case basis. 

If you have swelling in your armpit that doesn’t go away in a few weeks, or it gets bigger, or you have a lump in your breast or strong family history, consult your doctor. But if the timing works [i.e. you have recently received the COVID-19 vaccination], and you have no other concerns — no lump in the breast, you feel well — don’t be too anxious, because chances are it is related to the vaccine.