Severe cytomegalovirus gastritis and hypogammaglobulinemia in a patient treated with pembrolizumab.

A 66-year-old man with stage IVB oesophageal carcinoma treated with cisplatin, 5-fluorouracil, and pembrolizumab developed gastric erosions and ulcers with lymphoplasmacytic and neutrophilic infiltrates suggestive of immune checkpoint inhibitor-induced gastritis. High-dose steroids yielded transient relief. Cytomegalovirus (CMV) DNA was later found in gastric biopsies; steroids were withdrawn, and 3 weeks of intravenous ganciclovir led to partial improvement. Subsequent haemorrhagic gastritis raised concern for underlying immunodeficiency; serum immunoglobulin G (IgG), IgA, and IgM were undetectable. Administration of intravenous immunoglobulins (0.8 g/kg) produced rapid clinical resolution. This case report underscores the need for tissue-based CMV testing and cautious steroid use in severe gastritis.