Lymphadenopathy after COVID-19 vaccination in patients with endocrine cancer

The Covid-19 vaccination has been rapidly implemented among patients with cancer. We present two cases of patients with endocrine tumours who developed lymphadenopathy following a Covid-19 vaccination. In the case of a patient with multiple endocrine neoplasia (MEN) 1 syndrome, an 18-fluorodeoxyglucose (18FDG)-PET/CT showed positive axillary lymph nodes. Further work-up with fine needle aspiration showed a reactive pattern following a Covid-19 vaccination in the ipsilateral arm shortly before the 18FDG-PET/CT. A second patient, in follow-up for thyroid cancer, developed clinical supraclavicular lymphadenopathy after a Covid-19 vaccination. Follow-up ultrasound proved the lesion to be transient. These cases demonstrate lymphadenopathy in response to a Covid-19 vaccination in two patients susceptible to endocrine tumours and metastatic disease. With growing evidence about the pattern and occurrence of lymphadenopathy after mRNA Covid-19 vaccination, recommendations for scheduling and interpretation of imaging among cancer patients should be implemented to reduce equivocal findings, overdiagnosis, and overtreatment, while maintaining a good standard of care in oncological follow-up.