Increased 18F-FDG uptake in the axillary lymph nodes of the vaccinated side associated with COVID-19 vaccination

A 50-year-old female patient underwent 18F-FDG PET/CT following modified radical mastectomy for cancer of the left breast. Ten days before the PET/CT, the COVID-19 vaccine was injected intramuscularly into the right deltoid muscle. Increased 18F-FDG uptake of SUVmax (11.0) was observed in the lymph nodes of the right axilla, which had not been observed in the previous PET/CT. The size of the oval-shaped lymph nodes was up to approximately 11 × 9 mm; however, it was larger than that observed on the previous PET/CT. We contemplate that the increased FDG uptake was a reactive change in the lymph nodes associated with the COVID-19 vaccine.