Introduction: Immune-check-point blockade agents are extendedly used in the oncology field. Lower tract gastrointestinal toxicity is more frequent for anti-CTLA-4 than for anti-PD-L1, the target of Nivolumab. However, the immune-mediated gastritis or the esophagitis remain sporadic adverse events. In our center, two cases of acute pangastritis have been reported in six months.

Methos: We carried out a retrospective and descriptive study. We reviewed the clinical history of patients who received Nivolumab for any indication from January 2017 to December 2021.

Results: Two of the 100 patients treated with Nivolumab started with intense epigastric pain after its 9^th dose. Their characteristics are summarized in the table. Preferential ODG were performed, showing an intense inflammation with extense ulcerations throughout the stomach. Pathological analysis revealed epithelial neutrophilic infiltration, cellular apoptosis and crypt microabscesses, all related to Nivolumab drug- induced pangastritis. No form of Helicobacter pylori was identified. Double-dose of proton-pump inhibitor and cessation of immunotherapy was established, becoming the first patient rapidly asymptomatic. The second patient remained hospitalized with IV corticosteroids, achieving her complete recovery.

Conclusions: Nivolumab is used in metastatic, locally advanced or recurrent malignant diseases. It leads to the activation of the cytotoxic immune response against tumour cells. Immune-mediated gastritis can appear several months after its beginning but also after its discontinuation. The differential diagnosis must exclude infectious gastritis, vasculitis, Crohn's disease or Behçet syndrome. H. pylori infection can worsen its course. Medical approach is based on the immunotherapy cessation, gastric acid suppression and corticosteroids in severe cases. Infliximab has been successfully used in refractory patients.