Severe gastritis in a patient treated with immunotherapy: immune-mediated or reactivation of cytomegalovirus?

Cancer patients receiving programmed death 1 (PD-1) immune checkpoint blockade therapy are susceptible, due to immunosuppression, to a variety of infections including cytomegalovirus infection. We report an unusual case of histologically confirmed gastritis due to cytomegalovirus infection in a patient who had metastatic melanoma and received PD-1 blockade therapy with pembrolizumab. Pembrolizumab was discontinued and treatment with intravenous ganciclovir and oral vangaciclovir was initiated; the patient's symptoms improved significantly.