Immunotherapy Drug Pembrolizumab Linked to Rare but Serious Type 1 Diabetes

A young man being treated with pembrolizumab for kidney cancer with suspected lung metastases developed severe symptoms after 22 treatment cycles. He experienced extreme fatigue and a dangerous condition called metabolic acidosis, where his blood became too acidic. His blood sugar was markedly elevated, and his C-peptide levels were extremely low—a sign that his pancreas was no longer producing insulin effectively.

Doctors diagnosed him with immune checkpoint inhibitor-associated fulminant Type 1 diabetes (FT1DM). After receiving fluids and starting insulin therapy, his condition improved and he was discharged. Notably, he continued receiving pembrolizumab for three more cycles before the treatment was permanently stopped.

While pembrolizumab is widely used to treat solid tumors like melanoma and lung cancer, serious side effects like diabetes have been uncommon enough to go largely unnoticed. A review of published literature identified 32 confirmed cases of pembrolizumab-associated fulminant Type 1 diabetes. Most of these patients had lung cancer or melanoma.

The diabetes developed at different points during treatment, ranging from as early as the first cycle to as late as the 24th cycle. This variation suggests that timing is unpredictable and doctors cannot rely on a standard window to watch for the complication.

Among the 32 cases reviewed, two important patterns emerged. First, thyroid dysfunction—such as hypothyroidism or thyroiditis—occurred before or at the same time as diabetes in 90% of cases. This suggests that thyroid problems may be an early warning sign and that regular thyroid monitoring could help catch immune-related complications sooner.

Second, patients who tested positive for GADA (glutamic acid decarboxylase autoantibody), a marker of autoimmune diabetes, tended to develop fulminant Type 1 diabetes earlier than those without this antibody. This finding hints that some patients may be at higher risk based on their immune profile, though more research is needed to understand why.

Pembrolizumab works by releasing the brakes on the immune system so it can fight cancer. However, in rare cases, this can cause the immune system to also attack the insulin-producing cells in the pancreas. Fulminant Type 1 diabetes is a particularly severe form that develops rapidly and can cause serious complications like metabolic acidosis if not treated promptly.

For patients receiving pembrolizumab, this case series underscores the importance of close monitoring for symptoms like extreme fatigue, unusual thirst, or frequent urination. Doctors should also regularly check thyroid function and blood sugar levels. If you are being treated with pembrolizumab, discuss these potential warning signs with your medical team and do not hesitate to report new symptoms.

Source: Frontiers in endocrinology. 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.