COVID-19 Vaccination-Induced PET/CT False Positives in a Patient with Melanoma: A Case Report and Literature Review

Abstract

Background: COVID-19 vaccination may produce transient hypermetabolic lymphadenopathy that complicates oncological imaging and can resemble metastatic disease. Case Presentation: A 45-year-old woman with a history of superficial spreading melanoma of the left forearm underwent PET/CT for staging two weeks after receiving a non-replicating adenoviral vector COVID-19 vaccine (AstraZeneca®). Imaging demonstrated two FDG-avid left axillary lymph nodes and an incidental hypermetabolic pancreatic lesion. Pancreatic MRI and endoscopic ultrasound-guided fine-needle aspiration confirmed an intraductal papillary mucinous neoplasm. Because the axillary findings raised concern for melanoma metastasis, re-excision of the tumour bed and possible axillary lymphadenectomy were considered. A conservative approach was adopted, with re-excision and repeat PET/CT. At two months after vaccination, axillary uptake had regressed. Owing to persistent patient anxiety, sentinel lymph node biopsy was performed and demonstrated reactive adenitis without malignancy. Discussion: The temporal association with vaccination, ipsilateral nodal distribution, spontaneous metabolic regression, and benign pathology supported vaccine-associated lymphadenopathy. The reviewed literature similarly describes transient nodal uptake after COVID-19 vaccination that may be misinterpreted as cancer recurrence. Conclusion: Vaccination history, including vaccine type, date, and injection site, should be documented before oncological imaging. Where clinically appropriate, short-interval reassessment and multidisciplinary review may reduce unnecessary invasive procedures while ensuring that suspicious findings remain appropriately evaluated.