Immunotherapy and Type 1 Diabetes: A Rare but Serious Connection

A woman in her 50s was being treated with pembrolizumab—an immunotherapy drug—along with chemotherapy for triple-negative breast cancer. On day 125 of treatment, she came to the emergency department with fever and difficulty moving. Tests revealed she had developed fulminant Type 1 diabetes, a severe form of the disease triggered by the immune system.

Fulminant Type 1 diabetes is different from typical Type 1 diabetes because it develops extremely rapidly. The woman received immediate treatment with intravenous fluids and insulin, and her symptoms improved quickly. She was discharged after 17 days in the hospital.

Fulminant Type 1 diabetes caused by pembrolizumab is uncommon, occurring in fewer than 1 in 1,000 patients receiving the drug. However, despite its rarity, this condition is serious because it progresses so quickly that it can lead to diabetic ketoacidosis—a life-threatening condition—if not treated promptly.

Pembrolizumab works by activating the immune system to fight cancer cells. Sometimes, that heightened immune response can mistakenly attack the body's own healthy cells—in this case, the insulin-producing cells in the pancreas. This type of side effect is called an immune-related adverse event, or irAE.

The case study emphasizes that patients and doctors need to stay alert. Regular monitoring of blood glucose and awareness of symptoms like fever, weakness, and unexplained fatigue can help catch this condition early, when treatment is most effective.

If you or a loved one is receiving pembrolizumab or similar immunotherapy drugs, it's important to know that Type 1 diabetes is a possible side effect, even though it's uncommon. Work with your medical team to include regular blood glucose checks in your monitoring schedule.

Pay attention to unusual symptoms—especially fever, sudden weakness, or extreme thirst and urination—and report them to your doctor right away. Early detection and prompt treatment can prevent serious complications and allow you to continue your cancer treatment plan.

Source: Gan to kagaku ryoho. Cancer & chemotherapy. 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.