Fulminant type 1 diabetes mellitus induced by tislelizumab in a patient with lung adenocarcinoma: a case report.

[BACKGROUND] Although immune checkpoint inhibitor-related endocrine adverse reactions are common in clinical practice, fulminant type 1 diabetes induced by tislelizumab remains rare.

[CASE PRESENTATION] A 68-year-old Asian female patient was diagnosed with stage IV BRAF V600E-mutant lung adenocarcinoma via pleural biopsy in August 2020 and initially treated with dabrafenib and trametinib. In March 2023, she started treatment with tislelizumab owing to a new metastasis in the left lower lung. On 20 May 2024, the patient was admitted to the hospital with a 3-day history of the sudden onset of dry mouth, polydipsia, and polyuria, accompanied by mild nausea and vomiting. Laboratory examination results showed hyperglycemia, ketosis, and mild metabolic acidosis, but HbA1c was mildly elevated at 7%. The C-peptide release test indicated severe insulin deficiency. She was diagnosed with fulminant type 1 diabetes, treated with intravenous insulin and fluid resuscitation, and discharged. A total of 6 months after discontinuing tislelizumab, her pancreatic function had not recovered.

[CONCLUSION] Tislelizumab can induce fulminant type 1 diabetes via immune-mediated mechanisms. Proactive monitoring of fasting glucose, HbA1c, and islet function is essential for patients with cancer receiving tislelizumab therapy.