Delayed hemorrhagic gastritis caused by immunotherapy in a patient With metastatic melanoma.

Pembrolizumab is a monoclonal antibody which targets the programmed cell death protein 1 (PD-1) receptor of lymphocytes. It is commonly used to treat many types of malignancies. Immunotherapy-related adverse events are relatively common and include pneumonitis, colitis and hepatitis. A rare side effect of immunotherapy is gastrointestinal (GI) bleeding secondary to hemorrhagic gastritis. Side effects from immunotherapy most commonly occur eight to twelve weeks after initiation of therapy but can vary from days after the first dose to even months later. We present a rare case of a patient with metastatic melanoma who had confirmed immune-mediated hemorrhagic gastritis which occurred after 23 cycles of Pembrolizumab. Biopsies for Heliobacter Pylori (H. pylori) and cytomegalovirus (CMV) were negative. The patient's immunotherapy was discontinued, and he was started on high dose steroids. The symptoms (nausea, vomiting, and abdominal pain) improved dramatically with a long steroid taper. An esophagogastroduodenoscopy (EGD) performed three months after hospital discharge showed improvement in gastric mucosa, but biopsies continued to show evidence of acute and chronic gastritis. As cancer patients continue to live longer with immunotherapy, it is important for all providers to be aware of the less common side effects of newer agents such as pembrolizumab.