Case studies of rare oncologic metastases are an important source of clinical data for health care professionals and researchers. While infrequent, the knowledge base and clinical recommendations derived from such cases aid in advancements in the field. As such, we aim to add five cases to the growing body of literature. The first two male patients, aged 69 and 73, were diagnosed with colon adenocarcinoma, suspected to be a second primary prostate carcinoma, following positron emission tomography-computer tomography (PET-CT). This suspicion was ruled out by prostatectomy and histopathological investigations, which instead found adenocarcinoma of colonic origin. The next two male patients, ages 63 and 68, were diagnosed, respectively, with metastatic pancreatic adenocarcinoma with cardiac metastases and metastatic melanoma with distant metastases to the pancreas. The final patient was a 73-year-old male diagnosed with metastatic breast cancer after a radiological investigation of suspected renal cell carcinoma.

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.