In the following report, we describe 11 patients with various diagnoses and different treatment statuses (newly diagnosed, receiving treatment, or follow-up) of oncological diseases (breast, lymphoma, melanoma, and head and neck cancers). The patients underwent PET-CT for disease staging or follow-up and it was noted that all patients had areas of hypermetabolic uptake in the axillary lymph-nodes of the ipsilateral upper extremity where the Pfizer-BioNTech coronavirus (COVID-19) vaccine was administered. Following further investigations, including an ultrasound (US), biopsies and an examination of medical records, it was concluded that these findings were the result of the vaccination and not a progression of pre-existing disease.