Fatal C-reactive Protein-less Sepsis with Anti-IL-6 Autoantibody Production after Administration of Durvalumab.

Durvalumab plus platinum-based chemotherapy is the first-line treatment for extensive-stage small-cell lung cancer. Immune checkpoint inhibitors (durvalumab) can cause immune-related adverse events (irAEs). We herein report the first case of fatal sepsis with anti-interleukin-6 autoantibody production following durvalumab administration. A 62-year-old woman with extensive-stage small-cell lung cancer received carboplatin-etoposide plus durvalumab chemotherapy. Serum C-reactive protein (CRP) levels decreased below the detection sensitivity post-treatment. She developed severe sepsis during maintenance durvalumab therapy; however, her serum CRP level did not increase. The serum tested positive for anti-interleukin-6 autoantibodies, which can cause CRP-less infections. Anti-interleukin-6 autoantibody production and subsequent sepsis without serum CRP elevation are possible irAEs.