Immune checkpoint inhibitor-induced diabetes mellitus: A case series from a large tertiary centre in the UK

Immune checkpoint inhibitors (ICI) have transformed oncology treatment. This study presents a case series of adults diagnosed with ICI-induced diabetes mellitus (ICI-DM) and evaluates the challenges involved in the diagnosis and management of this rare immunotherapy side-effect.

A single-centre case series from the UK involved individuals who developed new onset insulin dependent diabetes after ICI treatment between 2017 and 2026. Data were extracted from the electronic medical records (EPIC® Systems Corporation).

Thirteen individuals (61.5% male, median age: 61 years [IQR 45-71]) diagnosed with ICI-DM were included. The majority were from a White ethnic background (84.6%). Time from ICI start to ICI-DM presentation had a median of 4 months (IQR 2-18). Most (n = 9, 69.2%) presented with diabetic ketoacidosis (DKA), with two requiring intensive care. Importantly three cases of DKA were potentially avoidable with earlier insulin initiation. Diabetes autoantibodies were positive in 54.5% (5 with GAD65 and 1 with IA-2 antibodies) with median C-peptide levels at diagnosis 161 pmol/L (IQR 10-232). The mean HbA1c before ICI start was 40 $\pm$ 7 mmol/mol (5.8 ± 2.8%) climbing to 80 ± 15 mmol/mol (9.5 ± 3.5%) at diagnosis, within a median interval of 3 months (IQR 2-4).

It is essential to increase healthcare professional awareness of immunotherapy side-effects to achieve early recognition and prompt management. Increased use of capillary glucose testing and immunotherapy alert card can improve outcomes. Future studies can investigate the relationship between potential risk factors and predisposition to ICI-DM development.