Case Report: Zolbetuximab-induced gastritis with protein-losing gastroenteropathy and hypogammaglobulinemia: a case implicating IgA vasculitis.

Zolbetuximab (ZOL), a monoclonal antibody targeting Claudin-18.2, is a promising therapeutic agent for the treatment of advanced gastric cancer. We report the first case of ZOL-induced acute gastritis leading to protein-losing gastroenteropathy, characterized by severe hypogammaglobulinemia and hypoalbuminemia, possibly mediated by IgA vasculitis. A 41-year-old woman with metastatic Claudin-18.2-positive gastric cancer was treated with ZOL in combination with chemotherapy. On day 8 of the second treatment cycle, she developed severe gastrointestinal symptoms and immunologic abnormalities. Laboratory tests revealed marked hypogammaglobulinemia (IgG 193 mg/dL) and hypoalbuminemia (albumin 1.9 g/dL). Esophagogastroduodenoscopy showed severe acute gastritis, and biopsy specimens demonstrated infiltration of CD4 lymphocytes into the stroma and CD8 lymphocytes into both the epithelium and stroma, as well as IgA deposition along interstitial capillaries. Protein leakage from the stomach was confirmed by Tc-HSA-D scintigraphy. These findings suggest that ZOL-induced mucosal injury and increased vascular permeability, likely driven by an IgA-mediated vasculitic mechanism, contributed to the protein loss. The patient's symptoms and laboratory abnormalities improved with supportive care. Upon ZOL rechallenge, gastrointestinal symptoms and protein loss recurred in a milder form, reinforcing a causal relationship. This case highlights a novel pathophysiological link between ZOL-induced gastritis and systemic immunoglobulin loss, underscoring the importance of careful monitoring of serum protein levels during ZOL therapy. Further studies are warranted to elucidate the immune-mediated mechanisms and optimize management strategies.