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Common reported side effects of the COVID-19 vaccine have been body aches, nausea, chills and headaches. But one side effect could be mistaken as a possible sign of cancer.

Some women who receive the COVID-19 vaccine may experience axillary adenopathy, also known as swollen lymph nodes in the armpit. This could be confused for a sign of breast cancer for those who have a mammogram, ultrasound, or breast MRI shortly after being vaccinated.

Axillary adenopathy is rare in women with an otherwise normal screening mammogram. It has also been rarely reported following the administration of tuberculosis, influenza and human papilloma virus vaccinations. However, higher rates of axillary adenopathy have been reported with administration of both Pfizer-BioNTech and Moderna COVID-19 vaccines.

For patients receiving the Moderna COVID-19 vaccine, axillary swelling or tenderness was reported in 11.6% of patients following one dose and 16% of patients following the second dose. In the Pfizer-BioNTech COVID-19 trial, the side effect was reported in 58 more cases in the vaccinated group than the placebo group.

Moffitt Cancer Center researcher Olya Stringfield had a breast MRI one week after her first dose of the COVID-19 vaccine. While she didn’t think much of the discomfort under her arm a few days after the vaccine, the imaging revealed a lymph node under her armpit had tripled in size. An ultrasound later confirmed the findings.

The results were frightening for Stringfield, who undergoes routine screenings because she is at increased risk for breast cancer. “I spent half the day crying,” she said. “I was nervous since I am already high risk.”

Although Stringfield had her imaging elsewhere, she reached out to Dr. Bethany Niell, section chief of Breast Imaging at Moffitt, to discuss her scans.

“Breast radiologists regularly speak with our patients to ensure that they understand their results and our recommendations for follow up imaging or biopsies. We want to help ease their anxiety. That is especially important during these difficult times,” said Niell.

Because breast radiologists believe they will continue to see axillary adenopathy as more and more patients become vaccinated, the Society of Breast Imaging has established recommendations to manage axillary adenopathy in patients with recent COVID-19 vaccination.

Those recommendations include:

  • Obtaining COVID-19 vaccination status, timing and side (left vs. right arm) of vaccination on patient intake forms.
  • Assigning unilateral axillary adenopathy on screening exams a Breast Imaging Reporting and Database System Score (BI-RADS) of 0 to allow for further assessment and documentation of medical history, including COVID-19 vaccination.
  • For those who have received a COVID-19 vaccine within the last four weeks and have unilateral axillary adenopathy, consider a short-term follow-up exam four to 12 weeks after the second vaccine dose.
  • If axillary adenopathy persists after short-term follow-up, consider a biopsy to exclude cancer.

“The Division of Breast Imaging at Moffitt is following the Society of Breast Imaging guidelines,” said Niell. “We have begun documenting COVID-19 vaccine doses and injection sites for all breast imaging patients, so the breast radiologists have additional information regarding how best to manage these patients.”

Niell also recommends scheduling breast imaging prior to COVID-19 vaccination, whenever possible, especially if patients have not had a mammogram in the last year.

Stringfield is now waiting to have another ultrasound in March, five weeks after she received the second dose of the COVID-19 vaccine. If that ultrasound still shows a swollen lymph node, she will have a biopsy.

She says regardless of her outcome, she hopes the pharmaceutical companies will study axillary adenopathy better to help spare other women the anxiety and financial burden of additional testing she is going through.

“You are just trying not to freak out,” said Stringfield. “Women should follow the new guidelines and wait just a couple of extra weeks to have imaging if they get vaccinated.”