COVID-19 mRNA Vaccination-Induced Lymphadenopathy Mimics Lymphoma Progression on FDG PET/CT.

We present here a 72-year-old man with mantle cell lymphoma who has completed chemotherapy and achieved complete metabolic response to the therapy 10 months ago. Series follow-up FDG PET/CT scans have been negative for lymphoma. Current FDG PET/CT scan showed a new cluster of subcentimeter left axillary lymphadenopathy with avid FDG uptake. There was also focal FDG uptake in the left upper arm deltoid muscle and adjacent subcutaneous soft tissue, with no other abnormal FDG-avid lesion or suspicious CT image findings. The medical history revealed that the patient received COVID-19 mRNA vaccine 2 days before the FDG PET/CT examination.