Two autopsied gastric cancer cases of rare drug-induced pneumonia associated with nivolumab plus S-1 and oxaliplatin: a case report.

Background: Drug-induced pneumonia, especially immune-related adverse events, can sometimes be fatal, and it is crucial to seize the signs for early treatment. A clinical trial (ATTRACTION-4) reported no cases of grade 4 or 5 pneumonia or interstitial lung disease associated with nivolumab plus S-1 and oxaliplatin. However, we encountered two cases of fatal pneumonia induced by this regimen. Case Description: The two patients were in their 70s, male and diagnosed gastric cancer with peritoneal dissemination. The patient of case 1 underwent surgery and adjuvant chemotherapy nine years before. The patient of case 2 was diagnosed unresectable 6 months before and chemo naïve. Both patients received nivolumab plus S-1 and oxaliplatin for the dissemination. The onset of both cases occurred after the fifth dose of the regimen, and the responses to corticosteroids were transient and limited. Computed tomography showed bilateral consolidation and ground-glass opacities, seemingly similar to an organizing pneumonia pattern. Acute and organizing stages of diffuse alveolar damage were detected histopathologically. Despite showing notable antitumor effects, both patients had indications of interstitial pneumonitis before admission, such as elevation of C-reactive protein (CRP) and Krebs von den Lungen-6 (KL-6) levels and slight lung opacity or respiratory symptoms approximately 10 days before admission. Conclusions: Patients undergoing nivolumab plus S-1 and oxaliplatin should be closely followed up with imaging, evaluation of symptom including oxygen saturation, and serological marker analysis such as lactate dehydrogenase, CRP, and KL-6. Early detection of pneumonia leads to adequate cessation of chemotherapy and early treatment, and this can prevent severe adverse events.