Explainer: Enlarged lymph nodes are a known temporary reaction to COVID-19 vaccines, not a sign of breast cancer

Various social media posts claim that COVID-19 vaccination “may result in symptoms of breast cancer,” implying that it could cause breast cancer. Experts say while the inoculation may cause lymph node enlargement, it is a known reaction and will subside in weeks.

Various social media posts suggest that because COVID-19 vaccination “may result in symptoms of breast cancer,” the inoculation could be triggering the development of breast cancer.

These posts are often accompanied with an image showing the mammograms of swollen lymph nodes in breasts. The claims can be found on Facebook (here and here), and Twitter. These posts combined were shared over 200 times.

But the claim is misleading.

“There is no data suggesting that COVID-19 vaccination would cause breast cancer,” said Ava Kwong, clinical professor and chief of breast surgery division at the Department of Surgery at the University of Hong Kong (HKU).

Kwong explained that while COVID-19 vaccination has been reported to have caused axillary adenopathy (enlarged lymph nodes in the breasts), it should not be assumed that the symptom is a sign of breast cancer.

“When the body is exposed to an infection, or substance designed to trigger the body to react and build up an antibody against the infection such as a vaccine, adenopathy can be part of the reaction when antibodies are being formed,” she said.

It is one of the symptoms of breast cancer but there could be other reasons people develop the same or similar symptoms.

“So in short it is our immune system’s common reaction,” said Kwong.

Clinical assistant professor Michael Tiong-Hong Co at HKU’s Department of Surgery said, “it is impossible to interpret the images shown on the website as what we [medical doctors] usually do is to compare bilateral mammograms.”

Even when lumps or calcification are present, doctors still require a biopsy to confirm the nature of the lump or calcification, he explained.

Co said the enlarged lymph node is a result of local reaction to the vaccination and lymph node enlargement is not necessarily cancerous.

Enlarged lymph nodes is a more intense immune response of COVID-19 vaccination, according to an article featuring Lisa Mullen, an assistant professor and breast imaging fellowship director at Johns Hopkins University.

According to Mullen, the response will be resolved within a few weeks after vaccination.

In March, a U.S.-based nonprofit organization, the Society of Breast Imaging, published a report on the effects of COVID-19 vaccination on the enlargement of lymph nodes in the breasts. Moderna and Pfizer-BioNTech vaccines were observed to have higher rates of such reports.

In the report, one of the management guidelines for medical workers reads, “vaccines of all types can result in temporary swelling of the lymph nodes, which may be a sign that the body is making antibodies in response as intended.”

In Hong Kong, enlarged lymph nodes is listed as an uncommon side effect of the Comirnaty vaccine from Fosun Pharma/BioNTech, which occurs in 1 out of 100 people. It is, however, not listed as a side effect of the CoronaVac from Sinovac.

Misleading usage of images and false claims

This Facebook post claimed that mammograms showing swollen lymph nodes in the breasts were taken from women who have recently got vaccinated.  It suggests they may have “metastatic breast cancer traveling to the lymph nodes or lymphoma or leukemia.”

This claim appears to originate from an article posted on this website. Similarly, this tweet suggests that COVID-19 vaccines triggered the development of breast cancer.

The post reads in Chinese, “after vaccination, the breasts show symptoms of breast cancer. Could it be that the cancer growth inhibitors are being inactivated?”

Screenshot of a tweet claiming COVID-19 vaccines triggered the development of breast cancer.
A mammogram attached to one claim suggesting enlarged lymph nodes in the breast following COVID-19 vaccination.

But Annie Lab found that the photo attached in the claim on Facebook does not show mammograms after COVID-19 vaccination.

Through reverse image search, the same mammogram image was found in an article published by Sunnybrook Magazine in 2016. The article said that 3D mammograms were introduced to improve breast cancer screening.

Side-by-side comparison of the images in the misleading claim and its original source.

Another image attached in the misleading tweet came from a news report by Fox News about a new guideline to avoid false positive results of breast cancer following COVID-19 vaccination.

Annie Lab found the original footage of the TV news report through a keyword search of “FOX 13” and “mammogram” that can be seen at the rightmost bottom of the image in the misleading tweet.

Side-by-side comparison of the images in the misleading claim and its original source.