━━ Background. Fulminant type 1 diabetes mellitus caused by immune checkpoint inhibitors is a rare adverse event. In lung cancer, several cases have been reported in non-small-cell lung cancer. We herein report a patient with small-cell lung cancer who developed fulminant type 1 diabetes mellitus after administration of durvalumab. Case. A 71-year-old man with extensive-stage small-cell lung cancer (cT4N3M1b, stage IVA) with no history of diabetes mellitus received combination therapy of carboplatin, etoposide, and durvalumab on May 20XX. He became aware of anorexia and fatigue on day 27. He was diagnosed with fulminant type 1 diabetes mellitus caused by durvalumab with hyperglycemia of 761 mg/dl, positive urine ketones, and urinary C-peptide of 3.9 μg/ day on the second course of treatment (day 30). After his blood glucose level had been stabilized with insulin therapy, an additional three cycles of chemotherapy with carboplatin and etoposide were administered. A significant response was achieved, and the patient survived without disease progression. Conclusion. Fulminant type 1 diabetes mellitus caused by durvalumab for small-cell lung cancer is a rare but urgent immune-related adverse event that requires attention.

━━ Background. The frequency of pseudo-progression caused by immune-checkpoint inhibitors in non-small cell lung cancer (NSCLC) is approximately 5%. Thus far, most reports of pseudo-progression in NSCLC have been due to immune-checkpoint inhibitor monotherapy. We report a case of pseudo-progression-like pleurisy after combined treatment with nivolumab and ipilimumab for lung adenocarcinoma. Case. A 70-year-old man with adenocarcinoma (pT3N0M1a, stage IVA) with pleural dissemination received combination therapy consisting of carboplatin, pemetrexed, nivolumab, and ipilimumab as first-line treatment. After treatment, he had fever, dyspnea, elevated CRP, and developed pleural effusion on the affected side. Thoracic drainage was subsequently performed. Abundant T lymphocytes with predominant CD4-positive cells infiltration were observed in pleural fluid cell-block specimens. Afterwards, his symptoms improved. No further accumulation of pleural effusion was observed, even though he continued receiving chemotherapy. Hence, he was diagnosed with pseudo-progression rather than an immune-related adverse event (irAE). Conclusion. This is the first report of pseudo-progressionlike pleurisy in a lung cancer patient after combined nivolumab and ipilimumab treatment. It is important to distinguish pseudo-progression from irAE-induced pleurisy.