Immune-related Adverse Effect after BNT162b2 Vaccination with Parallel Immune Checkpoint Inhibitor Therapy: A Case Report

COVID-19 vaccination is essential in cancer patients. However, there is limited evidence of the prognosis of these patients, especially for those taking immune checkpoint inhibitors (ICIs). We present a patient on pembrolizumab for advanced endometrioid adenocarcinoma experiencing continuous diarrhea and subsequent episodes of fever with pain in multiple joints following a second dose of the BNT162b2 mRNA COVID-19 vaccine. An ICI-induced immune-related adverse effect (irAE) was the main diagnosis; cytokine release syndrome and rheumatoid arthritis were also considered. Notably, the novel irAE occurred after the 19th pembrolizumab trial, highlighting the potential effect of changes in systemic immunogenicity after BNT162b2 vaccination. Ultimately, the patient was treated with steroid, which alleviated her symptoms. Here, we report a rare adverse effect after COVID-19 vaccination in an endometrioid carcinoma patient on ICI therapy. This report shows that there is a need to consider and investigate vaccine-related adverse events.