Immune checkpoint inhibitor-induced diabetes mellitus in metastatic NSCLC: a case report with extended follow-up and management considerations.

Immune checkpoint inhibitors-induced diabetes mellitus (ICI-DM) is a rare but potentially life-threatening endocrine immune-related adverse event, often characterized by abrupt onset of insulin deficiency and frequent presentation with diabetic ketoacidosis and difficulty with daily management with the available therapies. Lung cancer patients represent a substantial proportion of reported cases, reflecting the widespread use of PD-1/PD-L1 inhibitors in thoracic oncology. We report on the case of an elderly patient with metastatic lung adenocarcinoma treated with pembrolizumab who developed severe DM requiring permanent insulin therapy and leading to treatment discontinuation. The patient was subsequently followed over a prolonged period, during which oncological disease remained under sustained control despite immunotherapy interruption. We describe the clinical course, diagnostic workup, and multidisciplinary management, and review current guideline recommendations addressing acute metabolic management, diabetic treatment, and decision-making regarding continuation of immunotherapy. This case highlights the complexity of managing ICI-DM in real-world clinical practice. The current guidelines may help in broad terms. Although guidelines have been published, they remain cursory. Nevertheless, therapeutic decisions should ultimately be individualized through close multidisciplinary collaboration.