Immune Checkpoint Inhibitors and Type 1 Diabetes: A Rare but Important Connection

A man in his 70s with advanced lung cancer was treated with a combination of immune checkpoint inhibitor drugs—durvalumab and tremelimumab—along with chemotherapy. These drugs work by boosting the immune system to fight cancer cells. After his disease progressed, he switched to a different chemotherapy regimen and stopped receiving the immune checkpoint inhibitors.

Nineteen weeks after his last dose of ICI therapy, he developed fatigue and loss of appetite. Medical tests revealed that his body was no longer producing adequate ACTH (adrenocorticotropic hormone), a hormone that signals the adrenal glands to make cortisol. When his symptoms improved with cortisol replacement therapy, doctors recognized this as an immune-related adverse event triggered by his cancer treatment.

Five weeks later, the patient developed diabetic ketoacidosis—a serious condition where blood sugar becomes dangerously high and the body produces excess ketones. Further testing showed that his pancreas had largely stopped producing insulin, leading to a diagnosis of fulminant (sudden-onset) Type 1 diabetes, also believed to be related to his prior ICI therapy.

Immune checkpoint inhibitors work by releasing the brakes on the immune system, allowing it to attack cancer more effectively. However, this enhanced immune response can sometimes turn against the body's own organs and tissues, a phenomenon called an immune-related adverse event (irAE).

While these side effects are a known risk of ICI therapy, what makes this case particularly noteworthy is that two separate endocrine problems developed sequentially—first isolated ACTH deficiency, then Type 1 diabetes—and both occurred after ICI treatment had ended. This suggests that immune-related endocrine problems can develop months after a patient has finished cancer immunotherapy.

Cancer patients who receive immune checkpoint inhibitors need to be aware that immune-related adverse events are not limited to the active treatment period. This case highlights the importance of continued medical vigilance long after ICI therapy has stopped.

Symptoms of diabetes—such as extreme thirst, frequent urination, unexplained fatigue, and nausea—should be reported to a doctor promptly, even months after cancer treatment ends. Patients with a history of ICI therapy should discuss with their healthcare team whether long-term monitoring for endocrine problems is appropriate for their situation.

This is a case report describing one patient's experience. It documents a rare occurrence and does not mean that everyone who receives immune checkpoint inhibitors will develop Type 1 diabetes or other endocrine problems. The benefit of ICI therapy in treating advanced cancers continues to outweigh these risks for most patients.

However, this case serves as an important reminder that immune-related complications can be delayed and multifaceted. Healthcare providers and patients alike should remain alert to symptoms that could signal emerging endocrine disorders, even long after immunotherapy has concluded.

Source: BMJ case reports. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.