Stanford, CA—Women who receive COVID-19 vaccines have to consider an extra factor: when their next mammogram is scheduled.

Before scheduling an appointment for a screening, many breast care centers advise that patients wait 4 to 6 weeks after vaccination. The reason is that ipsilateral axillary lymphadenopathy (IAL)—essentially enlarged lymph nodes—after a COVID-19 vaccination can create diagnostic conundrums, according to a new report.

The research letter in the Journal of the American Medical Association Network Open says the condition should be managed in response to patient symptoms, imaging results, and risk factors.

Stanford Medical Center–led researchers searched radiology reports from March 19, 2021, to October 30, 2021, to identify women with recent COVID-19 vaccinations (6 weeks) and breast imaging–detected IAL, recording patient risk factors, symptoms, vaccination date, and vaccine manufacturer. The goal was to quantify the frequency and outcomes of breast imaging–identified IAL after a recent COVID-19 vaccination.

In the study, 3,008 of the 15,468 patients (19%) who underwent imaging had received recent COVID-19 vaccinations. Of those women (median age 53 years), 308 (10%) had postvaccination IAL detected. IAL was identified in 156 of the 1,834 patients who underwent screening mammograms (8%), 72 of the 883 patients who underwent diagnostic mammograms (8%), and 80 of the 291 patients who underwent MRIs (27%).

The frequency of IAL detections by vaccine manufacturers was 9% (172 of 1,836) for BioNTech-Pfizer, 12% (126 of 1045) for Moderna, and 5% (7 of 127) for Johnson & Johnson, with the manufacturer not known or reported for three patients.

Of the women with postvaccination IAL, 259 of the 308 (84%) without risk factors had clinical follow-up and were not referred for follow-up imaging. The remaining 49 patients with IAL (16%) were recommended to receive ultrasonography.

Most of the patients who developed the condition (64%) were found to have risk factors, including prior breast cancer (23 of 36 [64%]), suspicious ipsilateral imaging results (3 of 36 [8%]), current breast cancer (4 of 36 [11%]), or current regional malignant neoplasm (6 of 36 [17%]).

After ultrasonography a median of 4 weeks later, most patients with risk factors (65%) and without risk factors (54%) had resolution of their IAL. However, 18 patients (38%) showed persistent IAL "with decreased mean (SD) cortical thicknesses (5.2 [1.1] mm at baseline and 3.4 [0.3] mm at follow-up), consistent with resolving reactive lymphadenopathy. Of these 18 patients, four had current breast cancer and underwent sentinel lymph node excision (no metastases), one without risk factors was recommended for a second, 3-month follow-up ultrasonography, and 13 (8 with risk factors and 5 without risk factors) had biopsies owing to the presence of IAL assessed as BI-RADS (Breast Imaging–Reporting and Data System) 4A at follow-up (11 of 13 [85%]) or patient preference (2 of 13 [15%])," the researchers reported, adding, "All biopsies showed benign reactive lymphoid hyperplasia."

The findings are important, the authors noted, because more than 70% of U.S. adults have received COVID-19 vaccines. They called for evidence-based guidelines for postvaccination IAL.

"Although the reported frequency of IAL varies (3%-44%), our data on the frequency of IAL (10%) are similar to those reported for patients in clinical trials (14%). Our study provides a timely assessment of the management and outcome of IAL after COVID-19 vaccination," according to the researchers.

Even though it was not the case with their study, the authors urged follow-up for patients with risk factors to identify the small number of malignant neoplasms reported in other studies. Overall, they added, "Our study shows that IAL after COVID-19 vaccination is frequently a benign reactive finding, supporting expert society guidelines that individualize management approaches tailored to patients' risk factors, symptoms, and imaging findings."

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.