Immunotherapy-induced type 1 diabetes

Checkpoint inhibitors help the immune system attack cancer, but they can also turn it against healthy tissue, including the hormone glands. Diabetes develops in about 4 to 19 of every 1,000 people treated, according to 2025 Australian consensus recommendations endorsed by the Australian Diabetes Society, and a 2026 analysis of nearly 66,000 people put it at about 6 in 1,000. It is almost always linked to PD-1 or PD-L1 inhibitors, and the risk is higher when two checkpoint inhibitors are given together. It most often starts around 12 weeks after the first dose, but it can appear much later, and immune side effects can begin after treatment has finished.

Insulin production can fail quickly, so between about 1 in 3 and 2 in 3 people are first diagnosed with ketoacidosis (DKA), a medical emergency. Warning signs include strong thirst, passing a lot of urine, weight loss, unusual tiredness, nausea or vomiting, abdominal pain and fast breathing. Cancer services check blood glucose before each treatment cycle, and anyone with these symptoms should tell their cancer team straight away.

Diagnosis rests on a high glucose level with a low C-peptide level. Type 1 diabetes antibodies are found in only about half of people. Unlike some immune side effects, it does not get better when immunotherapy stops, and steroids do not reverse it, so treatment is insulin for life with care from an endocrinologist. Immunotherapy is usually paused while ketoacidosis is ruled out, and Australian cancer guidance allows it to be restarted once glucose is stable on insulin. A diabetes educator can help with insulin, glucose and ketone monitoring and a sick day plan.