Hypermetabolic Axillary Lymph Nodes Associated with COVID-19 Vaccination in Breast Cancer Management

A 42-year-old female patient diagnosed with invasive ductal breast ca underwent ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/ computed tomography (PET/CT) scan for staging, 1.5 cm diameter hypermetabolic lesion was observed in the lower inner quadrant of the right breast that was compatible with primary tumor [maximum standardized uptake value (SUV_max): 10.5]. No pathological ¹⁸F-FDG uptake was observed in lymph nodes whose fatty hilum was seen in the right axilla. However, in the left axilla and left deep axilla, hypermetabolic lymph nodes with a maksimum diameter of 19 mm and fatty hilum were observed (SUV_max: 8.0). In a detailed CT evaluation, these lymph nodes have thicker walls than the ones in the right axilla. The patient was questioned again and coronavirus disease-2019 (COVID-19) vaccination history (with BNT162b2, COVID-19 mRNA vaccine) was determined that was administrated to the left arm 5 days ago. Tru-cut biopsy was performed from the left aksillary lymph nodes and proved to be reactive lymphoid tissue and there was no primary or metastatic tumor in these axillary lymph node tissues. The patient was given neoadjuvant chemotherapy 4.5 months after the first ¹⁸F-FDG PET/CT, and the second was performed for the treatment response evaluation. Significant regression was determined from the findings. The patient underwent right total mastechtomy. She was being followed up with adjuvant chemotherapy and radiotherapy. In conclusion, hypermetabolic lymph nodes in the axillas should be interrogated for vaccination in patients with breast cancer. Hypermetabolic lymph nodes observed on the same side of the vaccinated arm in the ¹⁸F-FDG PET/CT scan may be related to vaccine-induced reactive lymph node enlargement. Lymph node metastasis may be excluded, especially if there are hypermetabolic lymph nodes with preserved fatty hilum in the contralateral axilla on the same side as the vaccinated arm. Active lymph nodes reactive to the vaccine become inactive after a while.